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~  *  Development  of  the  Nine-Banded  Armadillo 

-      from  the  Primitive  Streak  Stage  to 
i  i;  C  <r  Birtll .  with  Especial  Reference 

to  the  Question  of  Specific 
Polyembryony 

••'.I 

II.  H.  /NFAVMAN  AND  J.  THOMAS  PATTERSON 

From  «Ae  Zoological  Laboratory,  University  of  Texas 


FIFTEEN   TEXT   FIGURES   AND  NINE    PLATES 


Reprinted  from  the  JOURNAL  OF  MORPHOLOGY 
Volume  21,  No.  3 


L13RARV 


! 


THE  DEVELOPMENT  OF  THE  NINE-BANDED  ARMA- 
DILLO FROM  THE  PRIMITIVE  STREAK  STAGE  TO 
BIRTH;  WITH  ESPECIAL  REFERENCE  TO  THE 
QUESTION  OF  SPECIFIC  POLYEMBRYONY1 

H.  H.  NEWMAN  AND  J.  THOMAS  PATTERSON 
From  the  Zoloogical  Laboratory,  University  of  Texas 

FIFTEEN   TEXT   FIGURES   AND   NINE    PLATES 

CONTENTS 

I.  Introduction 360 

A.  Review  of  the  literature 360 

B.  Material  and  methods 363 

C.  Purpose  and  scope  of  the  present  paper 364 

II.   The  female  genitalia 365 

III.   Number,  arrangement  and  sex  of  embryos 367 

A.  Number  of  embryos 367 

B.  Airangement  of  embryos  368 

C.  Sex  of  embryos 370 

IV.  The  early  embryology 371 

A.  The  earliest  stages  of  Fernandez 371 

B.  The  primitive  streak  stage 374 

C.  The  five  to  seven  somite  stage 380 

V.  History  of  the  placenta 384 

VI.  History  of  the  amnion 393 

VII.  History  of  the  allantois  and  the  umbilicus 39& 

VIII.  Pairing  of  the  embryos 397 

IX.  Conditions  in  vesicles  containing  five  foetuses 401 

X.  The  question  of  identity  of  embryos 405 

XI.  Specific  polyembryony  and  the  determination  of  sex 406 

XII.  Summary  of  evidence  for  specific  polyembryony 409 

Bibliography 411 


1  Contribution  from  the  Zoological  Laboratory  of  the  University  of  Texas, 
No.  105. 

JOURNAL   OF   MORPHOLOGY,   VOI  .  21,    NO.  3. 


473380 


360  H.  H.  Newman  and  J.  T.  Patterson. 

I.     INTRODUCTION 
A.  Review  of  the  Literature 

It  is  not  our  present  purpose  to  attempt  any  comprehensive 
review  of  the  literature  dealing  with  the  development  of  the 
Edentata,  nor  even  of  that  treating  especially  of  the  armadillos. 
It  seems  advisable,  rather,  to  limit  our  survey  to  those  contri- 
butions, a  knowledge  of  which  is  essential  to  an  understanding 
of  the  problem  of  specific  polyembryony. 

That  certain  species  of  armadillos  bring  forth  at  a  birth  young 
all  of  one  sex  has  been  known  for  over  a  century.  According 
to  Azara,2  a  writer  of  the  eighteenth  century,  the  natives  of 
Paraguay  and  of  the  Argentine  Republic  knew  that  this  was  true 
for  the  Mulita  (Tatu  hybridum).  Any  observant  hunter,  who 
had  been  fortunate  enough  to  capture  a  litter  or  two  of  young 
animals  in  a  burrow  with  the  mother,  might  readily  have  noted  such 
a  unique  state  of  affairs,  for  the  sexes  are  easily  distinguishable. 

In  the  latter  part  of  the  nineteenth  century  Herman  von  Jher- 
ing,  ('85  and  '86),  met  with  similar  statements  on  the  part  of 
the  natives  of  Brazil  and  was  sufficiently  interested  to  attempt 
a  scientific  confirmation  of  what  had  been  until  then  merely  an 
interesting  piece  of  folklore.  Two  pregnant  females  came  under 
his  observation,  the  uterus  of  each  of  which  contained  eight  male 
foetuses,  all  in  exactly  the  same  stage  of  development.  Each 
foetus  was  described  as  having  its  own  separate  amnion:  but  all 
were  surrounded  by  a  common  chorion. 

These  conditions  were  interpreted  in  a*  subsequent  paper  by 
the  same  author  as  indicating  the  origin  of  the  several  embryos 
from  a  single  fertilized  egg,  and  it  was  further  assumed  from  the 
facts  in  hand  that  the  splitting  of  the  original  single  germ  into 
separate  embryonic  primordia  occurred  at  some  period  after 
fertilization.  Von  Jhering  apparently  saw  nothing  more  funda- 
mental in  this  situation  than'  the  discovery  of  a  new  type  of  ani- 
mal reproduction  to  which  he  gave  the  name  "temnogenesis." 
Its  bearings  on  the  problems  of  sex  determination  and  of  heredity 

2  Referred  to  by  von  Jhering. 


Development  of  the  Nine-Banded  Armadillo.          361 

were  not  appreciated.  To  him  however  belongs  the  credit  of 
having  discovered  specific  polyembryony  in  the  Mulita. 

No  attempt  was  made  to  secure  evidence,  either  internal  or 
external,  of  the  validity  of  von  Jhering's  suggestion  until  Rogner, 
('01),  took  up  the  subject  in  connection  with  his  studies  of  human 
monochorial  twins.  On  the  basis  of  a  histological  examination 
of  the  ovaries  of  one  pregnant  female  of  the  South  American  nine- 
banded  armadillo  he  attempted  completely  to  discredit  the  idea 
that  the  several  embryos  of  a  litter  arise  from  a  single  fertilized 
ovum.  Since  his  observations  strike  at  the  very  foundations  of 
the  question  of  polyembryony  in  the  armadillos  it  seems  neces- 
sary to  review  his  work  in  some  detail. 

The  genitalia  of  two  pregnant  females  were  sent  to  him  by 
von  Jhering,  and  an  examination  showed  that  the  ovaries  of  only 
one  specimen  were  sufficiently  well  preserved  to  admit  of  histo- 
logical examination.  Sections  of  the  other  pair  of  ovaries  showed 
that  a  large  -percentage  of  follicles  contained  more  than  one  egg. 
There  were  in  all  52  large  follicles :  11  with  2  eggs,  7  with  3,  2  with 
4,  1  with  5,  and  1  with  7.  The  two  largest  follicles  contained  four 
eggs,  exactly  the  number  necessary  to  produce  the  four  embryos 
habitually  brought  forth  in  a  litter  of  this  species.  Since  the 
youngest  follicles  never  contained  more  than  one  egg  the  condi- 
tions seen  in  the  older  ones  must  have  resulted  from  secondary 
fusions  of  adjacent  follicular  walls,  which  subsequently  disap- 
peared in  such  a  way  as  to  form  a  common  cavity.  The  author's 
figures  are  evidently  accurate  representations  of  actual  observa- 
tions and  are  calculated  to  convince  the  reader.  Especially  strik- 
ing is  the  figure  of  a  reconstruction  of  a  series  of  sections  through 
a  large  pluriovular  follicle  in  which  each  of  the  eggs  has  its  own 
thick  coating  of  discus  proligerus  cells. 

Rosner  believes  that  the  observed  condition  of  four  embryos 
surrounded  by  a  common  chorion  is  to  be  explained  by  the  fol- 
lowing sequence  of  events:  four  adjacent  follicles  fuse  in  such  a 
way  that  four  eggs  are  thrown  into  a  single  cavity ;  on  the  rupture 
of  this  compound  follicle  the  four  eggs  are  discharged  simultan- 
eously, descend  the  fallopian  tube  held  together  in  a  mass  by 
means  of  their  discus  proligerus  cells,  become  fertilized,  undergo 


362  H.  H.  Newman  and  J.  T.  Patterson. 

cleavage  and  come  to  a  common  point  of  attachment  in  the  uterus; 
subsequently  the  contiguous  walls  of  the  four  blastocysts  atrophy 
and  a  single  vesicular  chorion  is  produced. 

Were  Rosner's  observations  a  record  of  the  normal  conditions 
in  the  armadillo  ovary  the  question  of  specific  polyembryony 
would  assume  an  aspect  entirely  different  from  that  suggested 
by  von  Jhering,  and  we  would  need  to  seek  no  further  for  an  expla- 
nation of  the  observed  conditions.  The  observation  that  all  the 
embryos  in  a  litter  are  of  the  same  sex  was  summarily  dealt  with 
by  Rosner  who  considered  it  as  interesting  but  in  no  way  connected 
with  the  presence  of  a  common  chorion.  Fortunately  however 
there  is  now  every  reason  to  believe  that  Rosner's  material  was 
pathological  or  otherwise  exceptional,  for  no  subsequent  investi- 
gator has  been  able  to  find  in  the  armadillo  ovary  conditions  such 
as  he  described. 

Cuenot,  ('03),  while  engaged  in  the  study  of  the  problem  of  the 
determination  of  sex,  examined  the  ovaries  of  one  pregnant  and 
of  one  virgin  female  of  the  species  investigated  by  Rosner.  In 
the  ovaries  of  the  pregnant  specimen  there  occurred  only  one 
follicle  of  the  pluriovular  type  and  this  contained  only  two  small, 
rather  abnormal  ova.(j3ut  of  119  follicles  in  the  ovaries  of  the 
virgin  female  however  three  contained  two  or  three  eggs,  but  none 
was  found  with  the  number  requisite  to  give  rise  to  the  number 
of  young  habitually  born  in  a  litter. 

Until  quite  recently  no  further  progress  was  made  toward  the 
solution  of  the  problem.  In  1909,  however,  there  appeared  almost 
simultaneously  and  quite  independently,  two  contributions  to  the 
subject,  one  by  Fernandez,  (J09),  on  the  Mulita  (Tatu  hybridum), 
and  the  other  a  preliminary  report  by  the  present  writers,  ('09), 
on  the  North  American  armadillo  (T.  no vemcinctum) .  The  iwo  spe- 
cies evidently  agree  very  closely  in  many  of  the  more  fundamental 
details  of  development  but  differ  sufficiently  to  make  it  both  inter- 
esting and  valuable,  from  the  comparative  standpoint,  to  have 
the  developmental  history  of  both  species  worked  out  in  the  ful- 
lest detail. 

Fernandez  presents  somewhat  detailed  descriptions  of  seven 
rather  early  embryonic  stages  and  enters  upon  a  brief  discussion 


Development  of  the  Nine-Banded  Armadillo.          363 

of  some  of  the  more  important  questions  involved.  He  was  espec- 
ially fortunate  in  securing  in  a  good  state  of  preservation  two  very 
young  embryonic  vesicles  in  which  the  demarkation  of  the  several 
embryonic  primordia  had  not  yet  manifested  itself.  For  the  equi- 
valent of  this  stage  we  have  looked  in  vain  and  hence,. for  the  pre- 
sent at  any  rate,  are  compelled  to  rely  on  Fernandez's  description 
for  an  explanation  of  our  own  earliest  stages.  Since  it  is  neces- 
sary constantly  to  refer  to  Fernandez's  work  in  the  body  of  the 
text  no  further  comment  of  an  introductory  character  is  needed 
here. 

At  this  point  it  becomes  necessary  to  refer  to  our  own  pre- 
liminary report  in  order  to  correct  the  description  of  fig.  3  in 
that  paper.  The  specimen  there  figured  was  presented  to  us 
with  the  statement  that  it  was  intact  in  every  respect,  except 
that  the  uterus  and  the  contained  vesicle  had  been  slit  open  along 
the  mid- ventral  line.  On  the  basis  of  this  statement,  together 
with  a  study  of  the  external  features,  we  reconstructed  the  vesicle 
in  situ.  Our  subsequent  investigations  of  fresh  specimens  has 
led  us  to  suspect  that  what  we  took  to  be  a  young  vesicle  was  in 
reality  only  the  villous  portion  of  a  somewhat  later  stage. 

B.  Material  and  Methods 

During  the  past  two  years  we  have  had  the  opportunity  of 
examining  137  females  of  the  native  armadillo,  together  with  a 
considerable  number  of  males.  During  the  breeding  season  hun- 
ters employed  to  collect  material  for  us  covered  a  wide  range  of 
territory  in  south-central  Texas.  These  men  were  frequently 
obliged  to  haul  the  living  animals  through  rough  country  for  dis- 
tances of  fifty  miles  or  more  in  order  to  reach  an  express  office 
whence  they  could  be  shipped  to  our  laboratories.  As  a  rule 
a  number  of  days  elapsed  between  the  capture  of  the  annuals 
and  their  arrival  in  Austin.  This  delay  would  serve  in  part  to 
explain  our  ill  success  in  securing  the  earliest  embryonic  stages. 
In  order  to  obtain  a  complete  series  we  believe  it  will  be  necessary 
either  to  breed  the  animals  in  captivity  or  to  accompany  the  hun- 
ters on  their  expeditions  so  as  to  lose  no  time  in  examiningjfreshly 


364  H.  H.  Newman  and  J.  T.  Patterson. 

fertilizecjlfemales.  Although  we  fully  expect  to  secure  the  earliest 
stages  in  the  course  of  time  it  seems  inadvisable  for  us  to  post- 
pone the  publication  of  the  results  thus  far  obtained,  results  suffi- 
ciently clean  cut  in  themselves  to  form  the  basis  of  a  self-consis- 
tent and  fairly  well  rounded  embryological  account. 

At  present  we  have  in  our  possession  seventy  embryonic  vesicles 
comprising  a  close  series  of  stages  ranging  from  the  primitive  streak 
stage  to  birth. 

Little  need  be  said  about  the  methods  employed.  To  each  ani- 
mal that  reached  the  laboratory  was  given  a  number  and  a  page 
in  a  ledger  where  all  facts  that  might  be  of  interest  were  recorded. 
In  case  the  carcase  was  to  be  thrown  away  complete  records  of 
all  data  that  might  be  useful  in  the  future  were  kept.  The  ovaries 
of  the  majority  of  the  females  were  fixed  in  the  standard  cytologi- 
cal  fluids.  Every  part  taken  from  a  given  specimen  was  numbered 
accordingly.  Much  of  the  data  thus  gathered  proved  useful 
during  the  course  of  the  work  and  we  have  no  doubt  that  all  of  it 
will  ultimately  serve  to  throw  light  on  future  investigations. 

C.  Purpose  and  Scope  of  the  Present  Paper 

In  this  our  second  contribution  to  the  developmental  history  of 
the  armadillos  the  main  purpose  in  view  is  to  establish  the  fact  of 
specific  polyembryony  and  thus  to  clear  the  way  for  future  in- 
vestigation. A  more  or  less  tentative  explanation  of  its  causes 
and  of  the  conditions  and  relations  that  result  from  it  is  hazarded 
on  the  strength  of  the  evidence  now  in  hand,  which  is  internal  in 
contradistinction  to  that  derived  from  an  examination  of  the  ovar- 
ies and  testes,  no  detailed  discussion  of  which  is  attempted  at 
present. 

Although  the  question  of  polyembryony  is  the  central  problem 
it  is  impossible  to  treat  of  it  as  an  isolated  phenomenon  for  the 
reason  that  many  curious  developmental  processes  are  intimately 
associated  with  it.  The  history  of  the  amnion  and  of  the  placenta, 
for  example,  would  be  indecipherable  apart  from  the  fact  of  poly- 
embryony, and  the  inter-relationships  of  the  embryos  admit  of 
a  rational  explanation  on  no  other  basis.  The  associated  phenome- 


Development  of  the  Nine-Banded  Armadillo.          365 

non  of  germ  layer  inversion  is  also  (indissolubly)  bound  up  with  poly- 
embryony  and  in  turn  involves  many  peculiar  and  interesting 
relations. 

Any  adequate  treatment  of  the  principal  problem  will  therefore 
necessitate  the  presentation  of  a  somewhat  complex  array  of 
facts  whose  combined  verdict  will,  we  trust,  establish  our  main 
contention. 

Except  in  the  case  of  the  two  earliest  stages  described  no  at- 
tempt is  made  to  present  a  detailed  account  of  the  organogeny  of 
the  species.  No  doubt  such  a  study  would  reveal  many  facts 
of  interest  to  the  specialist  in  mammalian  embryology,  but  would 
serve  only  to  cloud  the  main  issue  with  obscuring  details. 


II.  THE    FEMALE    GENITALIA 

The  uterus  is  simple  and  not  unlike  that  of  the  primates  in 
form.  In  the  non-pregnant  condition  it  varies  somewhat  in  size 
and  shape  according  to  the  previous  history  of  the  individual. 
In  old  females  that  have  produced  a  number  of  litters  the  organ 
though  non-pregnant  may  be  distended  to  several  times  its  normal 
size,  often  leading  the  observer  into  the  vain  hope  of  finding  the 
earliest  stages.  The  uterus  of  the  virgin  adult  presents  a  less 
modified  condition  and  will  furnish  a  basis  for  the  accompanying 
detailed  description. 

The  average  dimensions  of  the  non-pregnant  uterus  are  as  fol- 
lows :  13  mm.  from  the  tip  of  the  fundus  to  the  junction  of  the  cer- 
vix with  the  vagina,  15  mm.  between  the  points  of  entrance  of 
the* two  fallopian  tubes,  and  10  mm.  deepdorso-ventrally.  Viewed 
from  the  dorsal  aspect  the  uterus  appears  to  be  broadly  kite- 
shaped  (fig.  7)  with  the  posterior  angle  blending  into  the  vagina. 
The  fallopian  tubes  are  approximately  straight  where  they  enter 
the  uterus,  but  near  the  ovaries  are  strongly  convoluted,  each 
ending  in  a  hood-shaped  fimbriated  infundibulum,  which,  with 
the  aid  of  a  posteriorly  directed  flap  of  the  broad  ligament, 
covers  a  large  part  of  the  ovary  and  thus  renders  the  escape  of 
the  ovum  into  the  body-cavity  well-nigh  impossible.  The  points 


366  H.  H.  Newman  and  J.  T.  Patterson. 

of  entrance  of  the  fallopian  tubes  are  about  equadistant  from 
the  tip  of  the  fundus  and  the  vagina,  thus  rendering  the  cavity  of 
the  uterine  body  much  larger  as  compared  with  that  of  the  cervix 
than  is  the  case  in  the  human  uterus,  where  the  tubes  enter  prac- 
tically at  the  distal  end  of  the  organ. 

The  ovaries  are  kidney-shaped  having  the  convex  side  directed 
anteriorly,  with  reference  to  the  axis  of  the  animal.  In  virgin 
females  the  two  ovaries  are  approximately  equal  in  size,  but  in 
individuals  that  are  or  have  been  recently  pregnant  there  is  always 
a  considerable  difference  in  the  size  of  the  two  ovaries.  The  larger 
one  may  be  two  or  three  times  as  large  as  the  smaller,  and  this 
greater  size  is  invariably  due  to  the  presence  of  a  single  enormous 
corpus  luteum,  the  actual  bulk  of  which  may  be  much  greater  than 
that  of  the  remaining  ovarian  tissue.  There  are  found  not  infre- 
quently smaller  bodies  (resembling  in  histo!6gical  appearance  the 
large  corpus  luteum)  which  are  crowded  to  one  end  of  the  ovary  and 
suggest  by  their  shrunken  and  irregular  form  that  they  are  either 
relics  of  a  previous  pregnancy  or  simply  the  lutea  of  ova  which 
were  never  fertilized.  It  may  be  stated  without  hesitation  how- 
ever that  there  is  never  more  than  one  large  and  prominent  corpus 
luteum  in  the  ovaries  of  a  pregnant  female. 

The  mucosa  of  the  uterus  is  undoubtedly  deciduate  in  charac- 
ter, as  may  be  seen  in  the  illustration  of  a  section  taken  from  a  series 
cut  through  a  pregnant  uterus  and  its  contents  (fig.  1).  Even 
at  the  comparatively  early  period  represented  it  can  readily  be 
seen  that  the  mucosa  is  separated  from  the  outer  layers  of  the  uterus 
by  a  lymph  space  of  considerable  magnitude. 

Since  the  young  embryonic  vesicle  always  gains  attachment  to  the 
mucosa  near  the  tip  of  the  fundus  it  is  not  a  difficult  matter  to 
orient  it  with  reference  to  the  uterine  axis.  It  will  be  found  con- 
venient to  refer  to  the  fundus  and  cervix  ends  of  the  vesicle,  the 
former  being  the  original  attached  and  the  latter  the  original  free 
end.  The  axis  of  each  embryo  is  also  related  to  that  of  the 
uterus,  in  that  its  anterior  extremity  is  directed  towards  the 
cervix  end  of  the  vesicle,  except  in  advanced  conditions  when  the 
length  of  the  umbilical  cord  occasionally  permits  an  embryo  to 
reverse  its  position  within  its  amniotic  sac. 


Development  of  the  Nine-Banded  Armadillo.  367 

The  pregnant  uterus  assumes  a  variety  of  shapes  in  different 
individuals.  At  approximately  the  same  period  of  pregnancy  it 
may  be  either  elongated  or  comparatively  broad,  either  blunt 
or  pointed  at  one  or  both  ends,  and  either  simple  or  clearly 
bilobed  dorso-ventrally  at  the  fundus  end  (figs.  42  and  43). 
These  various  forms  are  not  due  to  the  position  or  arrangement 
of  the  foetuses,  which  in  this  respect  are  practically  constant,  but 
probably  to  individual  variation  influenced  by  the  previous  func- 
tional history  of  the  organ. 


III.  NUMBER,  ARRANGEMENT  AND  SEX  OF  THE 
EMBRYOS 

A.  Number  of  Embryos 

In  sixty-five  out  of  seventy  cases  there  were  four  normal  embryos 
in  a  vesicle.  It  may  be  assumed  then  that  four  is  typical  for 
the  species.  Three  atypical  conditions  occurred  which  may  be 
listed  as  follows: 

1.  Vesicles  containing  five  normal  embryos  (three  cases,  nos. 
28,  91,  108). 

2.  Vesicle  containing  three  normal  embryos  each  measuring 
15  mm.  and  one  decidedly  abnormal  embryo  7  mm.  in  length 
(no.  57).    No  doubt  this  vesicle  was  destined  to  produce  a  three- 
embryo  litter. 

3.  A  case  of  twins  (no.  137  ).  These  were  born  in  captivity. 
A  very  careful  examination  of  the  uterus  and  intestines  of  the 
mother  convinced  us  that  there  were  no  other  young  born.    This 
may  have  been  a  case  somewhat  like  the  preceding  except  that 
two  embryos  degenerated  instead  of  one. 

There  appear  not  infrequently  in  otherwise  normal  embryonic 
vesicles  small  amniotic  sacs  that  usually  contain  the  more  or 
less  completely  degenerated  remains  of  what  may  once  have 
been  extra  embryos.  In  one  case  (no.  108),  a  vesicle  with  five 
normal  'embryos,  such  a  sac  appeared,  which,  if  truly  the  repre- 
sentative of  an  extra  embryo,  would  furnish  an  example  of  a  six- 


368  H.  H.  Newman  and  J.  T.  Patterson. 

embryo  vesicle.  In  another  case  (no.  17),  which  is  peculiar  in 
several  other  respects,  there  occurred  a  small  empty  amniotic 
sac  fused  firmly  to  the  wall  of  the  Trager  and  connected  with 
the  amniotic  sac  of  a  normal  embryo  by  means  of  an  amniotic 
canal  similar  to  those  of  the  other  embryos.  In  still  another 
case  (no.  9)  a  fairly  large  sac  in  the  Trager  region  was  connected 
by  means  of  a  perfect  amniofcic  canal  with  that  of  a  normal 
embryo  (fig.  44) .  There  is  little  doubt  but  that  these  sacs  repre- 
sent the  remnants  of  supernumerary  embryos  and  as  such  are 
the  equivalent  of  those  described  by  von  Jhering  and  Fernandez. 
It  is  interesting  to  note  in  this  connection  that  Tatu  novem- 
cinctum  shows  a  stronger  tendency  toward  stability  in  the  number 
of  foetuses  in  a  litter  than  does  T.  hybridum.  There  is  evident, 
however,  in  the  latter  species,  a  tendency  to  produce  eight  young 
in  a  litter,  just  twice  the  number  typical  for  our  species.  The 
numbers  of  individuals  in  a  litter  ranges,  however,  from  seven  to 
twelve. 

B.  Arrangement  of  Embryos 

In  order  to  clear  the  way  for  the  description  of  the  early  embry- 
onic conditions  it  should  provisionally  be  pointed  out  that  the 
four  embryos  of  this  species  are  arranged  in  pairs,  one  pair  to 
each  lateral  half  of  the  uterus.  The  upper  embryo  of  the  left 
hand  pair  usually  occupies  the  dorsal  amniotic  quadrant  and  is 
therefore  referred  to  as  the-"  dorsal  embryo  "  (no.  Ill) .  The  lower 
embryo  of  the  left  hand  side  occupies  the  left  lateral  amniotic 
quadrant  and  is  referred  to  as  the  "left  lateral"  embryo  (no. 
IV) .  The  lower  embryo  of  the  right  hand  pair  occupies  the  ven- 
tral amniotic  quadrant  and  is  the  "ventral  embryo"  (no.  I), 
while  its  mate,  occupying  the  right  lateral  quadrant  is  spoken  of 
as  the  "right  lateral"  embryo  (no.  II).  Nos.  I  and  II  constitute 
the  right  hand  pair  and  nos.  Ill  and  IV  the  left. 

The  orientation  of  the  vesicle  in  the  uterus  and  the  arrange- 
ment of  the  four  embryos  with  reference  to  the  vesicle  and  to 
one  another  is  rather  precise,  so  that  a  plane  running  from  the 
mid-dorsal  to  the  mid-ventral  line  of  the  uterus  would  divide 


Development  of  the  Nine-Banded  Armadillo.          369 


FIG.  1.  Outline  camera  drawing  of  a  transverse  section  through  a  pregnant 
uterus  measuring  about  15  mm.  long  by  14  mm.  wide.  Line  D  -V  is  drawn  from  the 
points  lying  at  the  middle  of  the  dorsal  and  ventral  sides  of  the  vesicle.  It  divides 
the  section  of  the  vesicle  into  halves.  Embryos  I  and  II  lie  in  the  left  hand  half,  and 
II  and  IV  in  the  right  hand  half.  a. a.,  line  of  attachment  of  the  amnion  to  the  ves- 
icle; e.v.,  a  small  extra  chorionic  vesicle,  which  is  not  fused  with  the  larger  one; 
i.L,  intestinal  loop;  l.s.,  lymph  sinus  between  the  wall  of  the  vesicle  and  the  uter- 
ine mucosa,  urn.  X  9. 


the  two  pairs  of  embryos  and  their  placental  areas  from  each 
other.  There  may  be  a  secondary  shifting  of  the  positions  of  the 
various  amniotic  sacs,  so  that  in  the  definitive  condition  one  may 
find  the  upper  embryo  of  the  right  hand  pair  occupying  the  dorsal 
position,  which  in  the  great  majority  of  cases  is  occupied  by  the 
upper  left  hand  embryo.  Such  a  shifting  might  easily  occur  at 
any  time  before  the  walls  of  the  various  amnia  fuse  firmly  with 
the  chorion,  a  process  that  does  not  occur  until  a  late  period  of 
gestation.  Previous  to  this  time  each  amnion  is  attached  to  the 
chorion  only  along  a  meridional  line,  an  attachment  that  would 
permit  the  whole  sac  to  swing  almost  as  readily  to  one  side  as  to 

JOURNAL   OF   MORPHOLOGY,  VOL.  21,   NO.  3. 


370  H.  H.  Newman  and  J.  T.  Patterson. 

the  other.  Reference  to  fig.  1  will  show  that  the  amnion  of  embryo 
II,  especially  after  the  amnia  have  increased  considerably  in 
size,  might  readily  overlap  the  line  D-V,  so  its  embryo  would 
occupy  the  dorsal  amniotic  quadrant.  The  same  shifting  might 
equally  well  occur  on  the  ventral  side.  Such  shiftings  might  take 
place  however  without  affecting  in  any  way  the  point  of  the  em- 
bryonic attachment,  which  is  immediately  adjacent  to  the  origi- 
nal amniotic  attachment  (fig.  1,  a. a.).  Such  departures  from  the 
typical  arrangement  of  embryos  in  the  vesicle  are  rather  rare, 
and  are  not  to  be  considered  as  of  prime  importance,  for  they 
in  no  way  affect  the  pairing  of  embryos,  a  relationship  depending 
on  the  point  of  attachment  of  the  latter  which  is  equivalent  to 
their  point  of  origin.  The  significance  of  this  arrangement  is 
discussed  in  a  subsequent  chapter. 

C.  Sex  of  Embryos 

In  thirty-eight  embryonic  vesicles  the  foetuses  are  sufficiently 
advanced  to  permit  of  the  accurate  determination  of  their  sex. 
There  is  no  exception  to  the  rule  that  all  embryos  in  a  vesicle  are 
of  the  same  sex. 

Although  the  armadillo  hunters  claim  that  males  are  consider- 
ably more  numerous  than  females  we  find  no  inequality  of  sexes 
in  the  sets  of  embryos  in  our  collection,  exactly  half  of  which  are 
male  and  half  female.  In  the  small  collection  of  nine  advanced 
sets  of  mulita  embryos  Fernandez  found  that  six  were  female  and 
three  male.  On  this  basis  he  proceeds  to  discuss  the  significance 
of  the  apparent  disproportion  of  sexes  in  the  species.  No  doubt 
a  larger  collection  of  embryonic  sets  would  have  shown  no  such 
disproportion,  for  in  our  earlier  survey  of  the  subject  of  sex  dis- 
tribution we  found  a  much  larger  proportion  of  males. 


Development  of  the  Nine-Banded  Armadillo.  371 

IV.  THE  EARLY  EMBRYOLOGY 

In  the  development  of  the  nine-banded  armadillo  we  find  that 
striking  peculiarity,  met  with  in  the  rodents,  of  germ-layer  inver- 
sion. In  the  case  of  the  armadillo  the  inversion  is  intimately 
bound  up  with  the  formation  of  the  four  embryos,  and  without 
it  the  mechanics  of  specific  polyembryony,  as  found  here,  would 
be  inexplicable.  The  possession  of  a  common  amnion  by  the  em- 
bryos at  an  early  stage  could  only  occur  as  a  sequence  to  inversion, 
and  strongly  suggests  that  the  embryos  are  the  product  of  a  sin- 
gle fertilized  egg. 

In  the  present' description  of  Tatu  novemcinctum  we  shall 
begin  with  the 'primitive  streak  stage,  and  leave  out  of  account 
the  younger  embryos  (except  for  a  brief  reference  to  the  work  of 
Fernandez)  until  we  shall  have  secured  a  series  covering  that  im- 
portant period.  In  dealing  with  the  following  stages  considerable 
emphasis  is  placed  upon  the  embryological  details,  and  especially 
upon  the  relations  existing  between  the  embryos.  This  is  done 
because  these  stages  furnish  the  strongest  internal  evidence  for 
polyembryony  that  has  been  brought  forward. 

A.     The  Earliest  Stages  of  Fernandez 

It  will  be  necessary  to  refer  to  the  work  of  Fernandez,  especially 
to  the  part  in  which  he  describes  his  youngest  two  stages;  because 
they  hold  the  key  not  only  to  the  morphology  of  the  older  embryos 
of  Tatu  hybridum,  but  also,  we  believe,  to  that  of  the  stage  of 
T.  novemcinctum  which  we  are  about  to  consider. 

Fernandez  secured  two  specimens  of  his  earliest  stage,  and  the 
one  he  describes  in  detail  was  cut  longitudinally  into  twenty- 
three  sections  (10  microns  thick).  It  was  found  attached  to  the 
mucus  membrane  at  the  bottom  of  a  fold  at*  the  fundus  end  of 
the  uterus. 

Fernandez  correctly  interprets  the  condition  presented  in  this 
early  stage  as  one  having  been  brought  about  through  the  process 
of  germ-layer  inversion,  and  compares  the  vesicle  to  corre- 


372  H.  H.  Newman  and  J.  T.  Patterson. 

spending  stages  of  the  rat  and  the  mouse,  described  respectively 
by  Selenka,  '84,  fig.  29,  Taf .  XIV.,  and  Melissinos,  '07,  figs.  38 
and  39  Taf.  XXXIV.  He  thus  finds  the  vesicle  composed  of 
three  sacs  lying  one  within  the  other:  the  innermost  one  is  the 
ectoderm,  the  middle  the  entoderm,  and  the  outer  the  tropho- 
blast  (hinfalJigen  Ectoderm),  which  at  the  proximal  or  attached 
end  of  the  vesicle  is  differentiating  into  the  Trager.  The  simil- 
arity between  the  vesicle  of  Fernandez  and  those  figured  by  Melis- 
sinos (his  figs.  38  and  39)  is  particularly  striking,  though,  as  he 
points  out,  there  are  several  differences.  In  the  first  place,  the 
mesoderm  is  not  yet  formed  and  the  so-called  Trager  cavity  scarce- 
ly can  be  regarded  as  homologous  with  that  of  the  mouse.  In  the 
second  place,  the  parietal  layer  of  the  yolk-sac  entoderm  is  not 
complete,  but  is  wanting  in  the  distal  portion  of  the  trophoblast. 
If,  however,  we  may  be  allowed  to  make  a  suggestion  based  on  a 
study  of  his  photograph  (fig.  6,  Taf.  XIX),  what  appear  to  be 
scattering  cells  lying  along  the  inner  surface  of  the  distal  tropho- 
blast might  well  be  interpreted  as  representing  the  remains  of  the 
parietal  layer  of  the  yolk-sac.  This  would  make  this  early  stage 
of  the  Mulita  very  closely  resemble  the  corresponding  stages  of 
several  other  forms,  as  illustrated  in  the  figures  of  such  investi- 
gators as  Selenka  ('84),  Robinson  ('92),  Jenkinson  ('00),  and 
Mellissinos  ('07). 

The  most  interesting  portion  of  this  young  vesicle  of  the  Mulita 
is  the  inner  sac,  for  it  is  the  primordium  out  of  which  the  ecto- 
derm of  the  several  embryos  later  differentia tes.  Fernandez 
points  out  the  significant  fact  that  it  gives  no  indication  of  being 
a  multiple  structure,  such  as  one  would  expect  to  see  if  the  vesicle 
were  the  product  of  the  fusion  of  several  eggs. 

The  second  stage  of  Fernandez  is  decidedly  more  advanced  than 
the  preceding,  and  was  found  lying  loose  in  the  fund  us  end  of 
the  uterus.  In  the  preserved  condition  it  measured  3  mm.  long 
by  2.3-2.5  mm.  wide.  The  general  condition  of  the  germ  layers 
in  this  vesicle  is  made  clear  in  the  slightly  modified  copy  of  his 
second  text-figure  (fig.  2).  The  figure,  which  is  a  diagram  of  a 
median  longitudinal  section  passing  through  two  embryos,  is 
shaped  like  a  horse  shoe.  The  entire  convex  anterior  and  lateral 


Development  of  the  Nine-Banded  Armadillo.          373 


ex.c. 


—  en 


— ec 


-am.  c.c. 


-V--m.p. 


— 777  S 


FIG.  2.  A  diagrammatic  longitudinal  section  of  an  early  stage  of  the  Mulita. 
ex.c.,  extraembryonic  body  cavity;  en.,  entoderm;  am.c.,  amniotic  cavity  of  the 
embryo;  am.c.c.,  beginning  of  the  amniotic  connecting  canal;  c.am.c.,  cavity  of  the 
common  amnion;  ms.,  mesoderm  ',m.  p.,  medullary  plate ;  i  r.  c.,  Trager  cavity;  tr.e., 
Trager  epithelium;  (slightly  modified  after  Fernandez). 


margins  represent  the  entoderm  of  the  inverted  yolk-sac,  while 
the  concave  posterior  margin  is  covered  with  Trager  epithelium. 
Between  these  two  regions  occurs  a  narrow  zone  where  the  vesicle 
was  attached  to  the  uterine  wall  (marked  X) . 

The  Trager  cavity  (tr.  c.)  is  situated  in  the  concave  space  roofed 
over  by  the  Trager  epithelium.  While  in  some  respects  this  cavity 
is  comparable  to  that  of  the  rodents,  yet  for  the  most  part  any 
such  comparison  would  appear  to  be  strained.  The  difficulty 
standing  in  the  way  of  pointing  out  any  true  homologies,  however, 


374  H.  H.  Newman  and  J.  T.  Patterson. 

must  be  attributed  to  the  incompleteness  of  the  history  of  these 
early  stages — a  fact  which  Fernandez  freely  admits. 

Within  the  limits  of  the  vesicle  there  are  two  distinct  cavities : 
one  the  general  cavity  of  the  vesicle  (ex.  c.),  and  the  other  the  com- 
mon amniotic  cavity  (c.  am.  c.).  The  former  is  lined  throughout 
with  mesoderm,  and  the  latter  with  ectoderm. 

The  embryos,  which  are  in  the  medullary  plate  stage,  lie  in 
pocket-like  diverticula  from  the  lateral  margins  of  the  floor  of 
the  common  amnion;  and  each  embryo  is  connected  with  the  lat- 
ter by  a  short  tube,  which  is  the  beginning  of  the  amniotic  con- 
necting canal.  The  common  amnion,  together  with  its  accom- 
panying embryos,  is  the  product  of  the  inner  ectodermal  sac  of 
the  earlier  stage.  It  is  not  at  all  easy  to  explain  fully  the  manner 
in  which  the  various  structures  presented  in  this  vesicle  develop 
out  of  the  primordia  of  the  preceding  vesicle,  although  the  history 
of  several  of  them  is  self  evident.  To  go  from  this  to  the  succeed- 
ing stage  is,  however,  an  easy  step,  and  we  shall  therefore  pass 
directly  to  it  as  exemplified  in  our  youngest  vesicle  of  Tatu 
novemeinctum. 

B.    The  Primitive  Streak  Stage 

We  were  fortunate  in  being  able  to  secure  from  the  uterus  the 
entire  embryonic  vesicle  in  practically  a  perfect  state  of  preserva- 
tion. The  opportunity  was  thus  afforded  not  only  to  make  a  de- 
tailed study  of  the  relations  existing  between  the  different  embryos 
but  also  to  obtain  a  drawing  of  the  vesicle  as  a  semi  transparent 
object  (fig.  12).  In  the  preserved  condition  it  measured  7  mm. 
wide  by  9  mm.  long.  It  is  slightly  flattened  dorso-ventrally  but 
in  general  outline  is  shaped  like  an  inverted  balloon,  with  two  lat- 
eral horn-like  projections  which  fit  into  the  openings  of  the  fal- 
lopian tubes.  These  horns  persist  for  a  considerable  time  and  are 
of  great  service  in  aiding  one  to  maintain  the  correct  orientation 
of  the  vesicle  during  its  early  development. 

The  surface  of  the  vesicle  presents  two  distinct  regions,  the 
lower  of  which  fits  into  the  fundus  end  of  the  uterus  and  is  recog- 
nized as  the  Trager.  It  is  therefore  covered  by  Trager  epithe- 


Development  of  the  Nine-Banded  Armadillo.  375 

Hum.  At  the  extreme  lower  end  there  is  a  small  cap-like  area 
where  the  primitive  attachment  knots  or  cords  of  the  Trager  epi- 
thelium are  beginning  to  disappear.  The  other  region  occupies 
the  upper  two-thirds  of  the  vesicle  and  differs  from  the  preceding 
both  in  its  greater  transparency  and  in  the  complete  absence  of  a 
trophoblast.  This  region  is  the  yolk-sac  of  the  inverted  type, 
and  consequently  is  covered  with  the  entoderm.  It  is  rather  in- 
distinctly divided  into  two  portions :  (1)  the  central  zone  occupied 
by  the  embryos  and  their  vascular  areas,  and  (2)  the  cap-like 
upper  third  in  which  the  almost  complete  transparency  is  ob- 
structed by  the  presence  of  the  common  amnion  and  its  connecting 
canals. 

Two  of  the  embryos  lie  on  the  upper  side  (corresponding  to  the 
ventral  side  of  the  uterus)  and  two  on  the  lower  side  of  the  vesicle. 
Each  embryo  is  connected  with  the  Trager  region  by  a  rather 
broad  band,  the  belly-stalk,  and  is  surrounded  by  an  amnion. 
Since  there  is  an  inversion  of  germ  layers,  the  embryos  when 
viewed  from  the  outside  of  the  vesicle  are  seen  from  their  ventral 
aspects;  hence,  the  posterior  portion  of  each  amnion  is  invisible 
except  as  seen  through  the  semi-transparent  embryo.  Anteriorly, 
however,  the  lateral  margins  of  the  amnia  are  clearly  distinguish- 
able and  are  seen  to  pass  forward  as  the  tube-like,  amniotic,  con- 
necting canals.  These  lie  on  the  inner  or  mesodermal  surface  of 
the  yolk-sac,  to  which  they  are  loosely  attached,  and  in  passing 
forward  they  converge  and  finally  enter  the  common  amnion. 
They  do  not  communicate  with  this  by  four  distinct  openings, 
but  by  two,  for  just  before  reaching  it,  the  canals  belonging  to  the 
dorsal  and  left  lateral  embryos  unite  to  form  a  single  tube,  as  do 
also  those  belonging  to  the  ventral  and  right  lateral  embryos. 
As  will  be  pointed  out  in  another  section,  this  fusion  of  the  canals 
is  an  indicatiqn  of  the  pairing  of  the  embryos  since  the  union  in 
each  case  is  between  individuals  of  a  pair. 

The  common  amnion  at  this  stage  is  a  comparatively  small 
vesicle  lying  at  the  extreme  cervix  end  of  the  vesicle.  The  man- 
ner in  which  this  condition  has  been  evolved  from  that  seen  in 
the  second  stage  of  Fernandez  is  not  difficult  to  figure  out.  On 
the  one  hand,  the  cavity  of  the  embryonic  vesicle  has  undergone 


376  H.  H.  Newman  and  J.  T.  Patterson. 

an  enormous  extension,  due  in  part  to  the  natural  growth  of  the 
vesicle  and  in  part  to  the  modification  in  the  shape  of  the  Trager 
wall,  which  has  changed  from  concave  to  convex;  on  the  other 
hand,  the  common  amnion  not  only  has  failed  to  keep  pace  with 
this  rapid  expansion  of  the  embryonic  vesicle,  but  has  actually 
ceased  to  grow  at  all,  and  is  destined  soon  to  degenerate  and  dis- 
appear. In  the  rapid  growth  of  the  embryonic  vesicle  the  embryos 
gradually  have  been  drawn  away  from  the  common  amnion, 
and  consequently  their  connections  with  it  have  been  pulled  out 
into  the  long,  slender,  tube-like  canals. 

The  embryo  viewed  from  the  dorsal  side  shows  the  exact  rela- 
tions existing  between  it  and  the  amnion  (fig.  13)-.  In  general 
outline  the  embryo  is  slipper-shaped  and  throughout  the  greater 
part  of  its  length  the  amnion  conforms  to  this  contour.  Both  an- 
teriorly and  posteriorly  the  amnion  narrows  down  rapidly — in 
the  former  direction  to  produce  the  amniotic  canal  (am.  c.  c.) 
and  in  the  latter  to  form  the  posterior  amniotic  process  (p.  am.  .p), 
which  ends  blindly  above  the  Trager.  The  level  at  which  the  am- 
nion becomes  narrower  than  the  belly-stalk  varies  in  different 
embryos.  In  the  embryo  in  question  it  cuts  in  some  distance 
posterior  to  the  mouth  of  the  allantois,  but  in  other  cases  it  may 
cut  in  at  a  level  somewhat  anterior  to  this  point. 

The  entire  embryo,  fr^m  the  anterior  end  of  the  medullary  plate 
to  the  posterior  tip  of  the  amnion,  measures  3.5  mm.,  but  the 
embryo  proper  is  only  2.5  mm.  long.  Running  through  the  cen- 
tral part  of  the  medullary  plate  is  the  elongated  primitive  streak, 
in  which  is  a  well  developed  primitive  groove  with  a  faintly  de- 
fined primitive  pit  at  its  anterior  end.  The  primitive  streak  is 
exactly  1  mm.  long,  and  has  at  its  anterior  end  a  distinct  head 
process  measuring  0.28  mm. 

The  outline  of  the  allantois  is  seen  through  the  embryo,  and 
begins  a  short  distance  back  of  the  posterior  end  of  the  primitive 
streak  and  extends  through  the  mesoderm  of  the  belly-stalk,  fi- 
nally ending  some  distance  anterior  to  the  tip  of  the  amnion.  Fer- 
nandez does  not  describe  the  development  of  the  allantois  in  the 
Mulita,  and  this  stage  is,  of  course,  too  far  advanced  to  give  any 
clue  to  the  exact  nature  of  its  origin. 


Development  of  the  Nine-Banded  Armadillo.          377 

Lateral  to  the  embryo  is  seen  the  beginning  of  the  yolk-sac  or 
vitelline  circulation.  At  this  time  the  blood  islands  are  well 
developed  and  incipient  blood  vessels  are  represented  by  a  net- 
work of  anastomosing  cords  of  mesoderm.  About  midway  be- 
tween any  two  contiguous  embryos  there  is  a  band-like  area  extend- 
ing from  the  Trager  to  the  upper  limit  of  the  area  vasculosa. 
The  band  represents  the  region  where  the  boundaries  of  the  vas- 
cular areas  of  adjacent  embryos  come  together,  and  thus  corres- 
ponds to  the  sinus  terminalis  of  other  forms,  except  that  it  is 
double  in  composition.  At  the  anterior  margin  of  the  vascular 
area  of  each  embryo  the  sinus  terminalis  tends  to  form  the  arc 
of  a  circle,  a  tendency  which,  if  not  inhibited  by  the  crowding  of 
four  embryos,  would  result  in  the  production  of  a  circular  sinus 
exactly  as  in  other  forms.  As  a  result  of  this  retardation  by  crowd- 
ing the  anterior  margin  of  the  vascular  zone  of  the  four  embryos 
is  in  the  form  of  a  series  of  scallops. 

For  an  appreciation  of  the  condition  of  the  germ  layers  it  is 
necessary  to  turn  to  a  study  of  representative  sections.  In  the 
most  typical  of  these,  such  as  that  taken  through  the  primitive 
pit,  the  neural  portion  of  the  ectoderm  is  thick  and  has  the  general 
appearance  of  that  of  corresponding  stages  of  other  forms  (fig. 
19).  The  outer  ends  of  the  section  curve  decidedly  upward, 
especially  the  one  on  the  right,  but  for  the  most  part  this  is  due 
to  the  fact  that  the  embryo  conforms  to  the  general  curvature  of 
vesicle.  At  the  ends  of  the  section  the  medullary  plate  turns  up- 
ward to  form  the  amniotic  ectoderm,  which  is  composed  of  a  single 
layer  of  cells. 

In  the  central  part  of  the  section  the  entoderm  is  composed 
of  rather  flattened  cells,  which,  however,  remain  distinct  from 
the  overlying  mesoderm.  Beyond  the  limits  of  the  primitive 
streak  it  becomes  thicker  and  its  cells  are  cuboidal  in  shape. 
It  must  be  kept  in  mind  that  the  entoderm  actually  forms  the 
outer  surface  of  this  region  of  the  vesicle;  for  the  trophoblast  has 
practically  disappeared  and  there  are  found  only  a  few  of  its  cells 
scattered  here  and  there  along  the  outer  surface  of  the  entodermal 
layer. 


378  H.  H.  Newman  and  J.  T.  Patterson. 

The  mesoderm  is  arising  from  the  primitive  streak  region  in 
the  characteristic  manner,  and  laterally  it  thins  out  and,  at  the 
point  where  the  ectoderm  turns  up  to  give  rise  to  the  amnion, 
divides  into  two  layers,  one  following  closely  the  amniotic  ecto- 
derm and  the  other  the  yolk-sac  entoderm. 

Through  the  middle  of  the  head  process  (fig.  18  h.  p.)  the  ento- 
derm at  the  center  of  the  section  is  barely  distinguishable  from 
the  mesoderm,  and  in  many  places  the  union  of  these  twro  layers 
is  very  intimate.  This  must  be  looked  upon  however  as  a  condi- 
tion which  is  in  all  probability  secondary.  In  the  region  of  the 
head  process  proper  the  mesoderm  cells  are  closely  packed  to- 
gether, but  are  entirely  separate  from  the  neural  plate. 

Anterior  to  the  head  process  the  mesoderm  rapidly  thins  out 
practically  to  a  single  layer  of  cells  and  is  easily  distinguishable 
from  the  entoderm  (fig,  17). 

Anterior  to  this  section  the  mesoderm  passes  into  a  thickened 
region  of  the  entoderm,  which  obviously  has  nothing  to  do  with 
the  mesoderm,  but  owes  its  existence  to  a  proliferation  of  ento- 
derm cells  (fig.  16,  p.  p.  h.).  It  was  not  detected  in  the  whole 
mount  preparations  of  the  embryos,  but  its  extent  is  easily  deter- 
mined by  a  study  of  sections.  The  thickening  runs  through  the 
first  five  sections  beginning  with  the  anterior  tip  of  the  embryonic 
shield,  and  its  width  is  equal  to  its  length,  and  it  therefore  forms 
a  circular  plate  about  45  microns  in  diameter.  In  every  respect 
this  circular  spot  corresponds  to  the  "protochordal  plate"  of 
Hubrecht,  (J08),  who  has  laid  especial  emphasis  upon  it  as  a  re- 
gion where  the  entoderm  is  clearly  a  source  of  mesoderm  forma- 
tion. Whatever  may  be  one's  conviction  regarding  Professor 
Hubrecht's  interpretation  one  can  at  least  be  certain  that  the 
thickening  is  purely  of  entodermal  origin  in  this  species.  Our 
series  is  here  too  incomplete  to  permit  of  tracing  out  the 
history  of  the  protochordal  plate,  and  thus  to  see  whether  its 
definitive  condition  is  simply  that  of  mesoderm  formation,  or 
whether  it  contributes  to  the  formation  of  the  fore-gut  or  the  oral 
plate. 

It  should  be  stated  here  that  the  protochordal  plate  at  the  stage 
under  discussion  thins  out  to  a  single  layer  towards  its  margin, 


Development  of  the  Nine-Banded  Armadillo.  379 

where  it  gradually  passes  into  the  surrounding  entoderm.  In 
many  places  the  mesoderm  cells  are  beginning  to  migrate  in  between 
the  plate  and  the  ectoderm,  and  especially  is  this  true  in  the  more 
anterior  sections  (fig.  21).  In  this  section,  which  shows  six  of  the 
mesodermal  cells,  the  anterior  limit  of  the  protochordal  plate  is 
represented.  A  very  short  distance  in  front  of  this  the  sections 
pass  through  the  amniotic  canal  (fig.  20),  which  is  seen  to  be  com- 
posed of  two  layers,  a  rather  thick  inner  ectodermal  layer,  and  a 
thin  outer  mesodermal  layer.  In  some  places  the  canal  is  loosely 
connected  with  the  underlying  mesoderm  of  the  yolk-sac,  but  for 
the  most  part  it  merely  lies  in  contact  with  the  latter.  * 

In  sections  lying  posterior  to  the  primitive  pit  there  is  nothing 
of  especial  note  until  we  come  to  the  region  where  the  allantoic 
tube  takes  its  origin.  The  mouth  of  the  allantois  is  in  the  form  of 
a  deep  groove  traversing  the  ventral  side  of  the  anterior  end  of  the 
belly-stalk  (fig.  22,  al) .  This  is  lined  with  an  especially  thick  ento- 
derm and  gradually  fades  out  anteriorly,  but  posteriorly  suddenly 
narrows  down  to  form  the  tube.  The  mesoderm  of  the  belly-stalk 
appears  to  extend  laterally  to  form  the  two  wing-like  processes, 
which  are  to  be  interpreted  as  representing  cross  section  of  the 
belly-stalk  bands  (b.  b.).  Externally  these  are  covered  with  an 
epithelium,  but  within  are  composed  of  a  loose  mesodermal  tissue 
in  which  run  the  umbilical  blood  vessels  together  with  their  accom- 
panying sinuses.  In  section  the  posterior  amniotic  process  is 
triangular  in  shape,  and  is  not  much  more  than  half  the  width 
of  the  belly-stalk. 

In  sections  taken  through  the  posterior  end  of  the  embryo 
(fig.  23)  the  allantois  is  reduced  to  a  slender  tube,  having  a  small 
lumen.  The  amnion  is  here  triangular  in  cross  section  with  the 
lower  angle  coming  in  close  proximity  to  the  allantoic  entoderm. 
The  mesoderm  has  much  the  same  shape  as  in  the  preceding  figure, 
but  may  be  divided  rather  indistinctly  into  two  portions:  (1)  the 
allantoic  mesoderm  which  surrounds  the  entodermal  tube,  and 
has  the  cells  compactly  arranged;  (2)  the  more  distal  wings  or 
belly-stalk,  bands  through  which  the  blood  vessels  run. 

The  semidiagrammatic  longitudinal  section  of  the  primitive 
streak  stage  is  shown  in  fig.  24,  and  in  connection  with  what  has 


380  H.  H.  Newman  and  J.  T.  Patterson. 

been  said  above  concerning  the  transverse  sections,  this  may  be 
studied  with  profit.  The  entoderm  in  this  section  can  be  traced 
from  the  protochordal  plate  back  along  the  entire  length  of  the 
embryo.  Throughout  the  greater  part  of  its  length  it  is  composed 
of  flattened  cells,  but  near  the  posterior  end  of  the  primitive  streak 
these  cells  become  cuboidal,  and  in  the  region  of  the  mouth  of 
the  allantoic  tube  (al)  take  on  a  columnar  appearance.  Posterior 
to  the  allantoic  opening  the  yolk-sac  passes  back  and  ends  abrupt- 
ly at  the  margin  of  the  Trager  epithelium  (tr.  e.}. 

WMle  the  median  section  does  not  show  the  lateral  belly- 
stalk  bands  which  form  the  main  connections  between  the  embryo 
and  the  Trager,  it  does,  however,  bring  out  with  clearness  the 
union  between  these  two  as  seen  at  the  extreme  tip  of  the  embryo. 
This  connection  (ms.  co.)  is  simply  a  backward  and  downward 
continuation  of  the  allantoic  mesoderm,  which  passes  over  into 
the  general  mesodermal  lining  of  the  Trager  region. 

C.     The  Five  to  Seven  Somite  Stage 

The  general  relations  existing  between  the  various  parts  of  the 
embryonic  vesicle  in  this  stage  closely  resemble  those  of  the  pri- 
mitive streak  stage,  but  the  vesicle  is  almost  twice  as  large, 
measuring  15  mm.  long  by  14  mm.  wide  (fig.  14).  Owing  to  this 
increase  the  horns  are  not  only  relatively  but  actually  shorter 
than  in  the  preceding  stage.  The  Trager  has  undergone  marked 
differentiation  and  shows  a  tendency  to  overgrow  the  yolk-sac 
region.  The  common  amnion  with  its  canals  presents  the  same 
general  features  as  before. 

The  most  interesting  changes  have  occurred  in  connection  with 
the  development  of  the  embryos,  and  it  is  to  these  that  we  would 
direct  attention.  In  the  first  place  emphasis  should  be  placed  upon 
the  fact  that  the  embryos  are  not  equally  differentiated,  for  the 
dorsal  and  left  lateral  have  each,  five  pairs  of  primitive  segments 
while  the  ventral  and  right  lateral  embryos  have  seven.  In  other 
words,  the  individuals  of  the  same  pair  are  in  the  same  stage 
of  development. 


Development  of  the  Nine-Banded  Armadillo.  381 

In  the  five  somite  embryo  (fig.  30)  the  neural  folds  have  not  yet 
coalesced  to  form  the  brain  vesicle,  and  consequently  the  neural 
groove  is  open  throughout  its  entire  length.  The  posterior  ends 
of  the  neural  folds  embrace  the  much  reduced  primitive  streak. 
The  embryos  are  bounded  laterally  by  an  area  pellucida,  which  is 
rapidly  being  invaded  by  the  blood  cords. 

In  sharp  contrast  to  this  embryo  is  the  individual  from  the  other 
pair  showing  seven  somites  (fig.  31),  and  unless  one  were  from  the 
first  aware  that  they  were  members  of  the  same  set  of  embryos, 
one  would  not  so  classify  them.  There  are  really  only  six  and  one- 
half  somites  in  this  embryo,  for  the  most  anterior  or  cephalic 
pair  is  connected  witn  the  head  mesoderm  and  is  somewhat  smal- 
ler than  the  succeeding  pairs  (fig.  15).  There  is  a  slight  indica- 
tion of  an  eighth  pair  being  cut  off  from  the  anterior  end  of  the 
unsegmented  paraxial  mesoblast. 

The  amnion  has  undergone  several  marked  changes,  chief  among 
which  are  (1)  its  enlargement  in  the  cephalic  region  of  the  embryo 
and  (2)  its  reduction  in  width  at  the  level  of  the  distal  part  of  the 
belly-stalk.  In  this  stage  the  neural  folds  have  risen  up  and  coal- 
esced to  form  a  portion  of  the  neural  tube.  The  point  where  the 
fusion  first  occurs  is  at  the  level  of  the  micUbrain  region,  and  from 
this  place  it  progresses  both  backwards  and  forwards.  The  anter- 
ior progress  of  the  union,  however,  takes  place  rather  slowly  and 
the  final  closing  on  the  under  side  of  the  fore-brain  to  form  the 
neuropore  does  not  occur  until  a  period  much  later  than  this. 

At  the  posterior  end  of  the  diverging  folds  the  reduced  primi- 
tive streak  is  seen  as  a  broad  plate,  which  in  the  mid-ventral 
region  is  slightly  concave,  and  by  transmitted  light  appears  to  be 
decidedly  thicker  than  the  lateral  portions.  The  notochord  is 
seen  to  arise  from  the  anterior  end  of  the  primitive  streak  and 
to  extend  forward  between  the  folds.  At  the  point  of  origin 
of  the  notochord  the  primitive  streak  is  unusually  thick,  forming 
a  distinct  primitive  knot,  just  back  of  which  is  the  suggestion  of 
a  primitive  pit.  At  the  posterior  end  of  the  primitive  streak  the 
entodermal  allantois  is  faintly  visible.  It  extends  backward 
lying  beneath  the  floor  of  the  posterior  amniotic  process,  and  falls 
far  short  of  reaching  the  tip  of  the  latter. 


382  H.  H.  Newman  and  J.  T.  Patterson. 

The  belly-stalk  now  shows  a  tendency  to  form  into"  two  bands 
at  the  proximal  or  attached  end.  Each  band  later  carries  an  umbil- 
ical artery  and  vein  from  the  placental  disc  to  the  embryo,  that  is, 
they  form  the  attachment  of  the  umbilical  cord  to  the  wall  of 
the  vesicle.  The  anterior  margins  of  the  bands  are  turned  up  to 
form  scroll-like  structures  beyond  which  the  scale-like  villi  of 
the  Trager  are  beginning  to  extend  out  over  the  yolk-sac  (fig. 

15  8.  V.). 

There  is  yet  to  be  considered  the  yolk  sac  circulation.  This 
consists  of  a  net  work  of  anastomosing  mesodermal  cords,  which 
in  section  are  seen  to  be  composed  of  a  central  mass  of  incipient 
blood  cells,  surrounded  on  the  upper  side  by  an  attenuated  layer 
of  mesoderm  and  on  the  lower  by  the  entoderm  (fig.  8,  b.  c.). 
These  cords  do  not  become  hollowed  out  even  at  a  much  later 
period  than  this.  Indeed  it  is  doubtful  whether  they  ever  become 
functional  blood  vessels. 

In  considering  the  details  of  structure  we  shall  confine  our  ac- 
counts to  a  brief  description  of  a  series  of  transverse  sections  of 
the  five  somite  embryo,  and  to  the  median  longitudinal  section 
of  a  seven  somite  embryo. 

In  the  region  of  the  neural  fold  the  neural  groove  has  become 
greatly  deepened  to  form  the  first  rudiment  of  the  brain  vesicle 
(fig.  26,  n.  g.),  and  the  lateral  margins  of  the  medullary  plate 
have  become  tucked  in  beneath,  thus  forming  a  bay  on  each  side 
that  is  at  once  recognized  as  the  lateral  extensions  of  the  head- 
fold  (  h.  /.).  In  consequence  of  this  folding  the  extreme  lateral 
portions  of  the  amniotic  cavity  have  had  the  marginal  parts  of 
the  medullary  plate  withdrawn  from  them,  with  the  result  that 
the  walls  of  the  amnion  have  more  or  less  collapsed,  obliterating 
the  cavity.  In  all  probability  the  obliteration  is  an  artifact,  due 
to  the  rapture  of  the  amniotic  canals  and  the  consequent  escape 
of  the  amniotic  fluid. 

In  the  central  region  the  entoderm  has  undergone  a  transfor- 
mation to  produce  the  notochord  (  n.  ch.)  which  consists  of  a  row 
of  columnar  cells.  Already  the  entoderm  shows  signs  of  beginning 
to  grow  beneath  the  notochord,  so  that  this  structure  will  soon 
be  cut  off  from  the  archenteron.  The  primordia  of  the  pharyn- 


Development  of  the  Nine-Banded  Armadillo.  383 

geal  pouches  (  ph.  p.)  are  seen  as  bays  of  entoderm  lying  on  each 
side  of  the  neural  tube. 

The  mesoderm  in  this  region  is  in  two  rather  distinct  forms; 
the  outer  portion  is  epithelial  in  character  and  conforms  to  the 
general  contour  of  the  entire  surface  of  the  section;  and  the  other 
part  is  composed  of  mesenchyme  and  lies  to  each  side  of  the  im- 
perfectly formed  brain  vesicle,  and  consists  of  scattering  stellate 
cells. 

The  medullary  plate  gradually  grows  narrower  as  one  passes 
backward  until  the  region  of  the  somites  is  reached,  where  its 
width  is  about  one-third  that  of  the  entire  embryo.  The  margins 
of  the  entoderm  have  almost  grown  together  beneath  the  noto- 
chord.  The  mesoblastic  somites  are  partly  constricted  off  from 
the  lateral  plates,  which  are  undergoing  the  process  of  splitting 
into  the  somatic  and  splanchnic  layers,  between  which  is  the  weak- 
ly developed  coelome. 

In  the  region  of  the  proximal  part  of  the  allantois  (fig.  28)  the 
belly-stalk  bands  are  very  much  folded,  having  their  outer  margins 
turned  up  to  form  the  scrolls  that  were  noted  in  fig.  15.  The 
umbilical  blood  vessels  in  the  bands  are  well  organized  and  are 
lined  with  an  endothelium.  The  only  other  structure  worthy 
of  special  mention  is  the  posterior  amniotic  process  which  is  re- 
duced to  a  small  flat  tube. 

The  final  section  of  this  series  to  be  considered  here  is  one  taken 
through  the  posterior  end  of  the  amnion  (fig.  29).  The  amnion 
and  median  posterior  portions  of  the  belly-stalk  bands  are  con- 
nected by  a  rather  slender  stalk  with  the  Trager  (ms.  co.).  The 
exact  nature  of  the  Trager  will  be  considered  in  another  section, 
and  it  remains  here  merely  to  point  out  that  the  original  primitive 
knots  are  being  rapidly  transformed  into  villi. 

The  longitudinal  section  of  the  seven  somite  embryo  (fig.  25) 
should  be  compared  with  that  of  the  primitive  streak  stage,in 
order  to  bring  out  the  most  significant  changes  occuring  in  devel- 
opment. The  notochord  lies  exposed  throughout  the  greater 
part  of  its  length,  but  at  each  end  it  is  covered  beneath  with  the 
entoderm.  At  the  posterior  end,  where  the  notochord  is  covered 
over,  the  entoderm  is  seen  to  turn  back  on  itself  for  a  short  dis- 


384  H.  H.  Newman  and  J.  T.  Patterson. 

tance  (fig.  25,  en').  This  is  doubtless  only  an  expression  of  the 
same  process  noted  in  the  study  of  cross  section,  in  which  it  was 
seen  that  the  entoderm  was  growing  in  beneath  the  notochord. 
The  primitive  streak  has  become  greatly  reduced,  due  to  its 
transformation  into  the  embryo.  The  final  change  to  which  we 
would  call  attention  is  seen  in  the  great  reduction  in  the  length 
of  the  allantoic  entoderm  (al) .  It  is  now  not  more  than  one-half 
of  its  former  length,  and  is  soon  destined  completely  to  disappear. 

V.     HISTORY  OF  THE  PLACENTA 

Certain  isolated  stages  in  the  development  of  the  placenta  have 
been  described  for  at  least  three  species  of  armadillo. 

Kolliker  (76),  Milne-Edwards  (78),  and  Duges  (79-'80), 
successively  described  the  placental  conditions  seen  in  rather 
advanced  vesicles  of  the  South  American  nine-banded  armadillo. 
Of  these  accounts  that  of  Milne-Edwards  appears  to  be  themost 
detailed.  The  embryonic  vesicle  is  described  as  being  a  pear- 
shaped  body  covered  with  a  chorion,  the  proximal  and  distal 
parts  of  which  were  thin  and  membranous,  while  the  middle  part 
formed  a  thick,  vascular,  four-scalloped  ring,  composed  of  four 
fused  placentae. 

A  stage  similar  to  that  just  cited  was  recently  described  in 
somewhat  greater  detail  by  the  present  writers,  (;09),  and  illus- 
trated with  two  diagrammatic  figures.  This  description  of  the 
North  American  variety  of  the  species  seems  to  agree  closely  with 
that  of  the  South  American  variety  as  given  by  the  authors  just 
referred  to.  No  doubt  we  have  essentially  the  same  species  on 
both  continents. 

The  only  other  reference  to  the  placentation  of  Tatu  novem- 
cinctum  is  that  of  Lane  ('09),  who  described  in  some  detail  the 
afterbirth  of  a  specimen  sent  to  him  from  central  Texas. 

A  more  comprehensive  account  of  placental  conditions  is  found 
for  Tatu  hybridum.  Von  Ihering  states  with  reference  to  an 
advanced  stage  of  placentation,  that  there  is  a  zonary  placenta 
which  has  nothing  in  common  with  that  of  the  carnivora,  but  must 
be  considered  as  a  "placenta  annularis  composita."  Each  of  the 


Development  of  the  Nine-Banded  Armadillo.          385 

eight  discoid  placentae  is  pressed  against  the  margins  of  the  two 
contiguous  ones  so  that  the  whole  set  forms  a  ring  or  zone 
encircling  the  vesicle  at  right  angles  to  the  long  axis  of  the  uterus. 

The  most  detailed  account  of  the  armadillo  placenta  yet  pub- 
lished is  that  of  Fernandez,  who  describes  several  important  early 
stages  of  this  structure  in  connection  with  his  account  of  the  early 
development  of  the  Mulita. 

Chapman  (;01),  gives  a  detailed  description  of  the  after-birth 
of  a  single  specimen  of  Dasypus  sexcinctus.  Excellent  figures  of 
all  structures  involved  accompany  the  text.  As  seen  from  the 
foetal  side  the  placenta  appears  to  be  truly  discoidal  in  form, 
but  on  the  maternal  side  the  distribution  of  the  villi  is  decidedly 
different  from  that  usually  found  on  that  type  of  placenta.  The 
markedly  arborescent  villi  are  arranged  in  a  broad,  somewhat 
lobose  ring  around  the  margin  of  the  disc,  leaving  the  centre  of 
the  latter  free  of  villi,  a  condition  strongly  reminding  one  of  a  much 
earlier  stage  in  the  development  of  the  placenta  of  Tatu  novem- 
cinctum,  when  the  original  saucer-shaped  Trager  has  begun  to 
produce  villi  along  the  free  overgrowing  margin,  but  has  a  com- 
paratively non-villous  central  area.  The  forked  connection  of 
the  umbilicus  with  the  placenta  is  almost  identical  with  that  found 
in  our  species.  In  view  of  these  striking  similarities  in  the  placen- 
tal  details  of  the  two  species  one  is  led  to  conjecture  that  the  con- 
ditions found  in  six-banded  armadillo  closely  approximate  the 
ancestral  conditions  of  the  more  highly  specialized  armadillos, 
of  which  Tatu  hybridum  seems  to  be  the  most  pronounced  exam- 
ple and  T.  novemcinctum  the  next. 

In  view  of  the  fact  that  there  has  yet  appeared  no  complete 
and  consecutive  account  of  the  history  of  the  placenta  of  any 
species  of  armadillo  it  seems  worth  while  to  devote  a  special  chap- 
ter to  a  description  of  the  conditions  seen  in  our  species. 

For  the  earliest  condition  it  will  be  necessary  once  more  to  call 
attention  to  the  youngest  embryonic  vesicle  of  Fernandez.  Here 
we  find  surrounding  the  true  embryonic  layers  the  trophoblast, 
which  is  attached  to  the  uterine  mucosa  by  means  of  a  thickened 
disc  or  plug  of  trophoblast  tissue,  called  the  Trager.  This  attach- 
ment disc  is  to  be  considered  as  the  primary  placenta.  As  the 

JOURNAL   OF   MORPHOLOGY,   VOL.  21,   NO.  3. 


386  H.  H.  Newman  and  J.  T.  Patterson. 

vesicle  develops  the  Trager  assumes  a  saucer-shaped  form,  as 
seen  in  vesicles  10  and  18  (figs.  12  and  14). 

It  will  have  been  noted  that,  owing  to  the  inversion  of  germ 
layers,  the  whole  yolk-sac  region  of  the  vesicle  is  covered  exter- 
nally with  entoderm,  and  that  the  trophoblast  layer  of  this  region, 
which  in  species  with  a  diffuse  placenta  ultimately  forms  the  outer 
lining  of  the  villi,  has  practically  disappeared.  In  the  Trager 
region,  however,  the  original  trophoblastic  epithelium  persists 
in  a  somewhat  modified  form.  This  region  of  the  vesicle  consists 
of  an  inner  layer  of  mesoderm,  at  this  time  rather  thin  and  free  of 
blood  vessels,  and  an  outer  trophoblastic  layer  of  true  epithelial 
character,  from  the  surface  of  which  protrude  branching  and  anas- 
tomosing cords  of  trophoblast  tissue,  which  give  to  the  Trager  a 
characteristic  rough  or  ridged  appearance  (fig.  12).  These  cords 
of  cells  appear  to  function  at  first  as  adhesive  pads  in  that  they 
no  doubt  serve  to  give  the  vesicle  a  firmer  grip  upon  the  uterine 
wall. 

In  the  primitive  streak  stage  these  Trager  cords,  when  exam- 
ined histologically,  show  themselves  to  be  composed  of  solid 
masses  of  cells  with  large  nuclei  and  deeply  staining  cytoplasm, 
surrounded  by  a  rather  flattened  layer  of  epithelium  continuous 
with  that  covering  the  general  surface  of  the  Trager.  Mitotic 
figures  are  of  frequent  occurrence  among  the  cord  cells,  showing 
rapid  cell  proliferation.  In  spme  respects  the  appearance  of  the 
tissue  suggest  a  glandular  function,  and  it  may  well  be  that  from 
it  a  secretion  is  given  off  which  subsequently  facilitates  the  pene- 
tration of  the  villi  into  the  uterine  mucosa.  That  these  cords 
of  cells  are  of  trophoblastic  origin  seems  certain,  for  the  meso- 
derm, the  only  other  layer  in  this  region  of  the  vesicle,  is  a  thin 
membrane  entirely  separate  from  the  trophoblast,  which  at  this 
period  it  has  not  begun  to  invade.  The  Trager  cords  then  must 
be  formed  by  a  process  of  rapid  local  cell  proliferation  which  causes 
masses  to  protrude  from  the  surface  and  frequently  to  overgrow 
it  to  such  an  extent  that  they  appear  to  be  almost  completely 
constricted  off  (fig.  9). 

Taking  the  primitive  streak  stage  as  the  last  phase  of  the  prim- 
itive placentation,  we  may  note  thac  the  Trager  occupies  roughly 


Development  of  the  Nine-Banded  Armadillo.          387 

one-third  of  the  area  of  the  embryonic  vesicle  (the  remainder 
consisting  of  the  yolk-sac  region),  that  the  embryos  are  attached 
to  the  Trager  by  paired  bands  of  mesoderm,  equivalent  to  the 
belly-stalk  of  the  primates,  and  that  the  central  area  of  the  Trager 
is  freer  from  thickenings  than  the  periphery. 

The  function  of  the  Trager  or  primary  placenta  appears  to  be 
not  so  much  nutritive  as  merely  adhesive,  since  tfiere  are  at  this 
time  no  blood-vessels  in  it  by  means  of  which  nutriment  might 
be  conducted  to  the  embryos.  It  is  highly  probable  that  whatever 
nutriment  reaches  the  embryos  comes  to  them  by  a  process  of 
osmosis  through  the  thin  wall  of  the  yolk-sac  region  of  the 
vesicle. 

The  formation  of  the  secondary  placenta  occurs  entirely  within 
the  confines  of  the  Trager  and  involves  at  tne  beginning  practi- 
cally its  whole  area.  A  very  instructive  stage  in  the  development 
of  the  placenta  is  seen  in  vesicle  18,  (figs.  14  and  15).  Here  the 
Trager  epithelium  has  been  pushed  out  into  short  scaly  villi, 
which  show  a  tendency  to  overlap  one  another  as  well  as  the  mar- 
gin of  the  yolk  sac  region.  These  protuberances  have  been  in- 
vaded by  a  stroma-like  mesencbyme,  which  has  arisen  from  the 
original  thin  mesodermal  epithelium  lining  both  Trager  and  yolk- 
sac  regions  of  the  vesicle.  The  free  ends  of  the  scale-like  villi 
are  tipped  with  masses  of  solid  gland-like  tissue  derived  by  the 
breaking  up  of  the  branching  cords  of  earlier  stages  into  numerous 
knots  which  are  carried  out  to  the  extremities  of  the  individual 
villi.  Although  the  general  Trager  epithelium  which  surrounds 
the  villi  has  persisted  in  the  form  of  a  rather  thick  syncytial  layer 
the  knots  are  bare  of  covering  except  for  the  presence  of  an  ex- 
tremely thin  layer  of  much  flattened  and  scattered  cells.  The 
knot  cells  therefore  are  in  a  position  to  come  into  most  intimate 
contact  with  the  uterine  tissues  and  probably  serve  as  organs 
of  penetration,  softening  the  maternal  tissues  by  means  of  a 
secretion  and  forcing  open  a  path  for  the  villi,  in  much  the  same 
way  as  the  diamond  tips  of  drills  cut  away  the  harder  materials 
and  open  up  a  path  for  the  shaft.  These  Trager  knots  forming  the 
tips  of  the  villi  appear  to  persist  throughout  almost  the  entire 
foetal  life  in  a  form  practically  identical  with  that  just  described. 


388  H.  H.  Newman  and  J.  T.  Patterson. 

The  tip  of  one  of  the  branches  of  an  arborescent  villus  is  shown 
in  fig.  11.  The  terminal  knot  of  cells  is  seen  to  be  practically 
naked,  while  farther  down  in  the  villus  are  shown  blood  vessels 
containing  nucleated  blood  cells. 

Although  the  formation  of  villi  occurs  at  first  over  almost  the 
entire  area  of  the  Trager,  somewhat  more  advanced  stages  clearly 
show  the  beginning  of  a  tendency  for  them  to  become  restricted 
into  four  distinct  patches  near  the  boundary  line  between  the 
Trager  and  yolk-sac  and  around  the  umbilicus  of  each  embryo. 
The  villi  of  other  regions  cease  to  grow  and  remain  short,  as  in 
fig.  3,  even  flattening  down  into  small  rounded  prominences 
which  probably  serve  no  nutritive  function.  Small  patches  of 
these  flattened  villi  are  scattered  over  the  central  area  of  the  Tra- 
ger as  well  as  between  the  newly  formed  placental  discs  of  the 
various  embryos. 

Diiring  this  period  the  Trager  area  of  the  vesicle  has  been  grow- 
ing more  rapidly  than  the  yolk-sac  region,  the  boundary  between 
the  two  remaining  at  all  times  definitely  marked.  In  fig.  3  is 
shown  semidiagrammatically  the  conditions  in  vesicle  11  in  which 
four  discoid  placentae  are  clearly  marked  off  from  the  surrounding 
areas  of  scattering  flat  villi.  At  this  stage  the  placentation  is 
obviously  discoid  for  each  embryo. 

In  vesicle  14,  (fig.  4)  a  decided  change  is  in  evidence.  The  four 
formerly  quite  separate  discs  have  undergone  a  considerable  in- 
crease in  diameter  and  have  come  into  very  intimate  contact 
along  contiguous  margins.  This  fusion  is  more  complete  between 
the  placentae  of  embryos  I  and  II  and  between  III  and  IV  than 
between  II  and  III  or  I  and  IV.  The  significance  of  this  is  dis- 
cussed later.  A  further  change  is  seen  in  that  the  villous  margin 
of  the  Trager  region  has  overgrown  the  yolk-sac  region  (not  fusing 
at  this  time  with  the  latter)  and  has  extended  the  placental  area 
of  the  vesicle  along  the  sides  of  the  cervix  cavity  as  far  as  the  os 
uteri.  Judging  by  the  size  and  abundance  of  the  arborescent  villi 
in  this  placental  annex  it  seems  obvious  that  it  plays  the  princi- 
pal nutritive  role  at  this  period.  One  might  compare  this  over- 
growing fringe  of  branching  villi  to  the  cricoid  placenta  of  Dasy- 
pus  sexcinctus. 


Development  of  the  Nine-Banded  Armadillo.          389 


IV 


FIG.  3.  A  semi -diagrammatic  representation  of  a  vesicle  seen  from  the  dorsal 
side.  II,  III,  and  IV  are  the  placental  discs  of  the  embryos  so  numbered.  Note 
that  those  belonging  to  the  paired  embryos  III  and  IV  are  closer  together  than 
II  and  III.  f.v.,  flattened  villi  of  the  Trager;  h.,  horn  of  the  yolk  sac.  X  2. 

FIG.  4.  A  semi-diagrammatic  drawing  of  the  dorsal  view  of  a  vesicle  slightly 
older  than  that  seen  in  fig.  3.  This  shows  the  fusion  of  the  placental  discs  I,  II,  III, 
and  IV  into  a  zone.  Note  that  the  fusion  between  the  discs  of  III  and  IV  (of  paired 
embryos)  is  more  intimate  than  between  II  and  III.  In  the  cervix  region  of  the 
vesicle  the  dorsal  part  of  the  overgrowing  placental  ring,  p.r.,  has  been  removed 
to  show  the  smooth  yolk-sac  lying  within  (y.a.}.  The  ring  was  fused  with  the  wall 
of  the  cervix  at  " z" .  The  dotted  line  lying  just  above  the  discs  represents  the  line 
along  which  the  upper  part  of  the  ring  was  cut.  X  2. 


The  yolk-sac  region  of  the  vesicle  is  from  this  period  on  cut  off 
from  all  contact  with  the  uterine  wall  except  at  the  mouth  of  the 
uterus  where  a  small  circular  area  remains  uncovered  by  any 
outer  layer.  This  condition  persists  until  birth  except  that  the 
overgrowing  ring  of  arborescent  villi  undergoes  a  gradual  degene- 
ration, as  the  placental  discs  increase  in  functional  prominence 
until  the  long,  branched  villi  become  mere  flattened  prominences, 
which  serve  only  to  slightly  roughen  the  membraneous  area  at 
the  cervix  end  of  the  vesicle. 


390  H.  H.  Newman  and  J.  T.  Patterson. 

The  fundus  end  of  bhe  vesicle  is  still  villous  to  some  extent,  but 
the  villi  are  so  small  and  scattered  as  to  interfere  only  slightly  with 
the  transparency  of  the  membrane.  One  can  readily  view  the  em- 
bryos in  situ  through  this  end .  Subsequently  the  villi  of  this  region 
disappear  entirely  with  the  exception  of  occasional  small  tufts 
that  might  readily  be  overlooked.  In  several  vesicles  (nos.  116 
and  117)  this  region  was  seen  to  be  four-lobed  owing  to  the  pre- 
sence of  two  thickened  bands  of  tissue  crossing  each  other  at 
right  angles  (figs.  37).  These  may  indicate  a  demarkationof  the 
several  embryonic  primordia  earlier  than  that  seen  in  the  differ 
entiation  of  the  embryos  themselves. 

Stages  intermediate  between  that  shown  in  fig.  4  and  the  defini- 
tive condition  can  best  be  shown  by  a  series  of  photographs. 

Fig.  34  shows  a  somewhat  older  vesicle,  in  which  the  area  at 
the  fundus  end  is  seen  to  be  smooth  and  almost  free  of  villi. 
The  lobing  of  the  composite  zonary  placenta  is  only  slightly 
marked. 

In  fig.  35  is  shown  the  cervix  end  of  a  stage  slightly  more  ad- 
vanced than  the  preceding  one.  The  heavy  coating  of  arbores- 
cent villi  is  seen  to  cover  the  entire  cervix  end  of  the  vesicle  with 
the  exception  of  the  small  area  that  lies  across  the  mouth  of  the 
uterus. 

The  dorsal  surface  of  another  vesicle,  approximately  of  the  same 
age  as  the  last,  is  seen  in  fig.  36.  The  vesicle  is  attached  to  the 
shrunken  cervix  of  the  uterus.  Here  is  evidenced  the  tendency 
on  the  part  of  the  composite  zonary  placenta  to  divide  into  two 
double  lateral  discs.  The  deep  notch  occurs  between  the  placental 
areas  of  embryos  II  and  III.  The  small  lobe  (d.  6.)  is  destined  to 
persist  as  a  bridge  between  the  two  lateral  discs. 

Two  farther  steps  in  the  development  of  the  definitive  placenta 
are  seen  in  figs.  38  and  39.  The  vesicle  has  grown  to  be  several 
times  the  size  of  that  shown  in  fig.  34.  Coincident  with  this  great 
increase  in  surface  the  villi  in  the  composite  zone  have  increased 
in  functional  importance  while  those  that  previously  over- 
grew the  yolk-sac  region  of  the  vesicle  have  degenerated,  leaving 
a  membraneous  area  at  the  cervix  pole,  which  in  time  becomes  as 
large  or  even  larger  than  that  at  the  other  end  of  the  vesicle. 


Development  of  the  Nine-Banded  Armadillo.  391 

In  fig.  40  is  seen  a  condition  slightly  more  advanced  than  that 
described  in  detail  in  our  preliminary  paper.  There  is  now  at 
each  pole  of  the  oval  vesicle  a  star-shaped  clear  area,  with  a 
broad,  deeply  notched  placental  zone  between,  which  still  shows 
distinct  signs  of  its  origin  from  four  discoid  placentae .  The  notches 
are  more  deeply  cut  along  the  dorsal  and  ventral  lines  than  along 
the  lateral,  where  the  placentae  of  the  paired  embryos  I  and  II 
and  likewise  III  and  IV  are  so  intimately  fused  as  barely  to  show 
the  points  of  union. 

Shortly  after  the  condition  just  described  the  placenta  takes  on 
what  appears  to  be  approximately  the  definitive  condition.  The 
tendency  to  form  two  well  defined  lateral  discs  is  carried  still 
farther,  but  in  no  case  have  we  observed  the  complete  separation 
of  the  two  placental  areas.  As  a  rule  the  bridge  between  the  two 
main  discs  is  narrower  on  the  dorsal  side  than  on  the  ventral,  but 
its  narrowness  is  compensated  for  by  the  presence  of  a  heavier 
coating  of  villi  and  by  that  of  rather  large  placental  blood-vessels 
which  serve  to  connect  one  main  disc  with  the  other.  It  seems 
to  be  almost  invariably  the  case  that  the  division  into  the  two  dou- 
ble lateral  discs  strikes  only  approximately  along  the  boundary 
lines  of  the  original  discoid  areas,  for  colored  injections  forced 
into  the  placental  vessels  of  individual  foetuses  run  across  the 
narrow  placental  bridges  and  invade  more  or  less  extensive  and 
clearly  marked  villous  areas  of  the  other  main  disc.  Such  a 
condition  is  well  shown  in  fig.  41. 

The  umbilical  cords  which  may  be  from  18  to  20  centimeters 
long  are  attached  rather  near  the  fundus  margin  of  the  placentae 
except  in  rare  -cases  where  five  foetuses  occur  and  involve  the 
crowding  of  one  or  more  unbilical  cords  away  from  the  margin. 

Although  a  litter  of  young  armadillos  was  born  in  the  laboratory 
we  were  not  fortunate  enough  to  secure  the  after-birth  and  there- 
fore cannot  describe  this  final  stage  of  the  placenta.  A  comparison 
of  the  size  and  degree  of  development1^  the  new-born  young  with 
the  oldest  foetuses  in  our  possession  convinces  us  that  the  condi- 
tions just  described  stand  as  definitive.  Yet  Lane  in  his  recon- 
struction of  the  after-birth  of  the  single  individual  under  observa- 
tion fails  to  find  connecting  bridges  between  the  main  discs.  He 


392  H.  H.  Newman  and  J.  T.  Patterson. 

may  have  observed  a  rare  case  in  which  the  line  of  separation  into 
lateral  discs  passes  exactly  between  the  placental  areas  of  the  two 
dorsal  and  the  two  ventral  embryos.  Moreover  we  find  no  such 
clearly  marked  non-villous  areas  at  the  two  poles  as  he  describes. 
The  smooth  area  at  the  cervix  end  is  in  all  of  our  specimens  very 
small  and  circular  in  outline,  while  that  at  the  fundus  end  is 
only  vaguely  outlined  and  frequently  shows  patches  of  flat 
villi. 

Any  attempt  to  classify  a  placenta  with  the  above  history 
meets  with  grave  difficulties,  as  one  might  conjecture  from  the 
multiplicity  of  terms  applied  to  it  by  different  writers.  Kolliker 
in  his  original  description  of  the  conditions  of  the  embryonic 
membranes  of  T.  novemcinctum  refers  to  the  placenta  as  disc- 
oidal  and  deciduafce.  Milne-Edwards  considers  it  to  be  com- 
pound zonary  in  structure.  Beddard  describes  it  as  dome-shaped 
and  deciduate;  while  Lane  suggests  the  term  "  zono-discoidalis 
indistincta,"  subdividing  StrahFs  class  " zono-discoidalis "  into 
two  varieties,  "distincta  and  "indistincta." 

Somewhat  similar  placental  conditions,  as  found  inT.  hybridum, 
are  designated  by  von  Jhering  as  indications  of  a  "placenta  annu- 
laris  composita."  Chapman's  use  of  the  term  "  deciduate  cricoid" 
appears  to  be  apt  for  the  placenta  of  the  six-banded  armadillo. 

Of  all  these  terms  the  one  that  appeals  most  strongly  as  des- 
criptive of  a  certain  rather  persistent  phase  in  the  development 
of  this  multiformed  structure  is  that  used  by  von  Thering,  "  plac- 
enta annularis  composita,"  but  one  must  not  forget  that  at  first 
it  is  simply  discoidal,  then  cricoid,  then  tetra-discoidal,  later 
annularis  composita,  and  finally  incompletely  doubly  discoidal. 

If  animals  are  to  be  classified  according  to  the  form  of  their 
placentae,  a  method  0f  classification  that  is  fortunately  falling  into 
disrepute,  it  would  be  very  difficult  to  classify  the  nine-banded 
armadillo,  unless  we  arbitrarily  decide  to  select  some  particular 
developmental  phase  of  the  placenta  as  a  criterion  for  classifi- 
cation. In  such  cases  one  would  be  led  to  chose  either  the  primary 
or  the  definitive  condition  and  would  thus  call  the  placenta  either 
"simply  discoidal"  or  "incompletely  doubly  discoidal."  Other 
terms  scarcely  find  a  rational  basis. 


Development  of  the  Nine-Banded  Armadillo.          393 

The  conjecture  that  the  compound  placenta  of  T.novemcinctum 
has  been  derived  without  any  fusion  of  "four  embryonic  vesicles 
from  a  condition  similar  to  that  described  by  Chapman  for  Dasy- 
pus  sexcinctus,  is  very  tempting  in  view  of  the  evident  close  rela- 
tionship of  the  two  species  and  the  striking  resemblance  that  exists 
between  them  in  the  details  of  the  placenta,  umbilicus  and  other 
structures.  This  if  true  would  furnish  one  of  the  most  cogent 
proofs  of  polyembryony,  since  we  find  in  the  more  highly  special- 
ized species  a  quadruple  placenta,  which  at  a  rather  early  period 
closely  resembles  the  definitive  placenta  of  a  more  primitive 
species  that  gives  birth  to  single  young  or  to  twins.3 


VI.    HISTORY   OF   THE   AMNION 

From  Fernandez's  description  of  his  earliest  stage  it  is  clear  that 
the  common  amniotic  cavity  is  at  first  the  hollow  of  the  ectoder- 
mic  vesicle,  which,  through  the  inversion  of  germ  layers,  has  come 
to  lie  within  an  envelope  of  entoderm.  Regional  differentiation 
of  this  ectodermic  vesicle  produces  the  ectodermal  portions  of  the 
embryonic  primordia,  which  are  at  first  contained  within  a  single 
vesicular  amniotic  cavity.  Subsequently  the  individual  embryos 
sink  into  pockets  in  the  floor  of  the  common  amnion,  which  has 
evidently  become  fused  to  the  walls  of  the  yolk-sac  at  the  cervix 
pole  of  the  embryonic  vesicle.  The  posterior  end  of  each  embryo 
has  become  fixed  by  means  of  the  primordium  of  the  belly-stalk 
to  the  margin  of  the  Trager,  and  consequently,  as  the  yolk  sac 
gradually  increases  in  size,  the  embryos  are  drawn  away  from  the 
common  amnion,  retaining  connection  with  it  only  by  means  of 
slender  tubes,  the  amniotic  connecting  canals  (figs.  12  and  14). 
It  has  been  shown  that  each  pair  of  embryos  withdraws  from  the 

3  We  are  informed  by  Mr.  Robert  D.  Carson,  superintendent  of  the  Philadelphia 
Zoological  Garden,  that  a  female  six-banded  armadillo  in  captivity  gave  birth  to: 

1.  A  single  male,  on  May  10,  1901. 

2.  Twin  males,  on  April  6,  1902. 

3.  Twins  (male  and  female),  on  July  19,  1902. 


394  H.  H.  Newman  and  J.  T.  Patterson. 

common  amnion  into  a  single  pocket  and  leaves  for  a  short  dis- 
tance a  single  connecting  canal.  Later  each  member  of  these  pairs 
loses  its  connection  with  its  partner  and  acquires  its  own  canal. 
This  secondary  separation  of  the  pairs  produces  a  forking  of  each 
of  the  original  two  connecting  canals,  a  condition  that  persists 
for  a  long  time. 

After  the  embryos  have  left  the  common  amnion  the  latter 
probably  becomes  functionless  and  ceases  to  grow.  Fortunately 
however  it  persists  with  all  of  its  connections  through  a  consider- 
able developmental  period,  furnishing  evidences  of  polyembryony 
and  of  embryonic  pairing.  In  fig.  44  it  is  shown  still  typical  in 
form  with  its  connecting  canals  entire  but  with  their  lumens  in- 
terrupted with  plugs  of  tissue.  The  regions  between  the  plugs 
have  become  distended  through  local  secretion  of  ammo  tic  fluid, 
so  that  the  canals  as  a  whole  present  a  decidedly  moniliform  appear- 
ance. In  fig.  45  a  somewhat  more  advanced  stage  of  degenera- 
tion in  these  structures  is  seen.  The  common  amnion  can  no 
longer  be  recognized  but  the  canals  are  still  clearly  defined. 
Each  of  these  shows  a  number  of  pronounced  bead-like  swellings, 
one  of  which  may  represent  the  remains  of  the  common  amnion. 
These  canals  may  persist  until  stages  as  advanced  as  that  shown 
in  fig.  33,  but  are  seldom  to  be  detected  in  later  stages. 

The  posterior  amniotic  processes,  which  in  early  stages  were 
seen  to  be  closely  associated  with  the  development  of  the  allan- 
tois,  do  not  persist  in  so  marked  a  form  in  our  species  as  in  the 
Mulita.  Only  in  rare  cases  does  one  see  any  traces  of  these 
structures  at  a  period  later  than  the  five  to  seven  somite  condition 
(fig.  15).  In  vesicle  17,  however,  one  of  the  embryonic  amnia 
is  connected  by  means  of  an  amniotic  canal  with  a  sac  as  large  or 
larger  than  the  common  amnion  but  lying  at  the  opposite  pole 
of  the  vesicle.  This  condition  is  no  doubt  exceptional  and  may  be 
accounted  for  on  the  supposition  that  the  posterior  amniotic 
process  of  one  of  the  embryos,  on  account  of  its  unusual  length, 
protruded  far  down  into  the  Trager  region,  came  into  contact 
with  and  united  with  it,  and  subsequently  swelled  into  an  amniotic 
sac  at  the  point  where  its  terminal  bulb  fused  with  the  Trager 
wall. 


Development  of  the  Nine-Banded  Armadillo.          395 

Another  exceptional  condition  is  that  seen  in  fig.  46,  where 
branching  from  a  typical  amniotic  canal  of  one  of  the  embryos, 
is  an  accessory  canal  running  to  an  empty  amniotic  sac  at  the 
center  of  the  Trager.  Such  a  condition  is  doubtless  due,  as  was 
stated  in  another  place,  to  the  presence  of  the  remains  of  a  degen- 
erated fifth  embryo.  Teratological  amniotic  structures  similar  to 
those  just  described  were  observed  in  a  number  of  other  cases. 
In  most  instances  there  seems  to  be  no  doubt  that  they  represent 
the  retarded  or  degenerate  remains  of  supernumerary  embryos. 
The  frequent  occurrence  of  similar  rudimentary  embryos  in 
Tatu  hybridum  and  in  our  own  species  seems  in  itself  a  strong 
piece  of  internal  evidence  of  specific  polyembryony,  for,  on  the 
basis  of  the  origin  of  the  several  embryos  from  separate  eggs,  it 
would  be  difficult  to  understand  why  some  should  develop  into 
complete  embryos,  and  others,  in  the  same  vesicle  and  under 
practically  identical  conditions,  should  meet  with  so  little  success. 

After  the  closure  of  the  lumens  of  the  various  amniotic  canals 
all  communication  between  the  four  or  more  amnia  is  cut  off; 
and  henceforth  each  embryo  has  its  own  separate  amnion  in  as 
true  a  sense  as  in  those  mammals  that  produce  several  entirely 
independent  young.  The  developmental  history  of  these  envel- 
opes is  moreover  in  no  important  way  different  from  that  of 
other  mammals  except  that  in  late  stages  a  gradual  fusion  occurs, 
first  of  all  with  the  wall  of  the  chorionic  vesicle  and  later  with  one 
another,  where,  through  the  pressure  of  growth  their  walls  have 
come,  into  contact. 

Various  representative  stages  in  the  later  history  of  the  amnion 
are  seen  in  the  photographs  herewith  presented.  In  fig.  44 
the  amnia  may  be  seen  to  lie  rather  closely  applied  to  the  bodies 
of  the  embryos.  In  fig.  33  the  cavities  of  the  individual  amnia 
have  increased  greatly  in  size  and  the  sacs  have  assumed  an  o\oid 
form  with  the  narrower  end  directed  toward  the  cervix  pole  of 
the  vesicle.  In  fig.  34,  an  external  view  of  the  fundus  end  of  a 
somewhat  older  vesicle,  the  amnia  are  seen  pressed  against  the 
membraneous  area  of  the  Trager,  producing  at  points  of  contact 
an  added  transparency,  reminding  one  of  windows  through  which 
the  embryos  can  clearly  be  viewed. 


396  H.  H.  Newman  and  J.  T.  Patterson. 

Even  after  the  embryos  have  reached  a  length  of  4  cm.  the  am- 
niotic  sacs  are  still  quite  free  from  one  another,  but  a  little  later 
they  begin  to  fuse  along  contiguous  surfaces.  Not  until  about  a 
month  before  birth  however  do  they  become  inseparably  bound 
together.  After  the  fusion  is  complete  the  amnia  occupy  the  entire 
cavity  of  the  vesicle  and  divide  it  into  (normally)  four  quadrants 
of  equal  size,  each  running  from  pole  to  pole.  This  nearly  defini- 
tive condition  was  described  in  detail  in  our  preliminary  account 
and  needs  no  further  attention  here.  In  fig.  46  the  edges  of  the 
amniotic  partitions  separating  adjacent  embryos  may  be  seen  at 
"a."  The  umbilical  cords  are  always  attached  just  to  the  left  of 
the  partitions. 

VII.    HISTORY  OF  THE  ALLANTOIS  AND  THE  UMBILICUS 

The  early  history  of  the  allantois  was  shown  to  be  very  inti- 
mately bound  up  with  that  of  the  belly-stalk  or  primitive  umbilicus 
This  intimate  connection  persists  as  long  as  the  allantois  retains 
a  distinguishable  structure.  In  stages  of  the  degree  of  advance- 
ment shown  in  vesicle  17  and  11  (figs.  1  and  44)  the  entodermal 
allantois  is  seen  as  a  slender  cord  of  cells  more  or  less  closely  fused 
with  the  umbilicus  and  showing  here  and  there  traces  of  a  former 
lumen.  The  outlines  of  the  mesodermal  allantois,  however,  are 
no  longer  distinguishable  from  the  tissues  of  the  belly-stalk.  The 
allantois  of  the  armadillos  seems  then  to  be  entirely  vestigeal 
in  later  stages  of  development. 

The  umbilicus  arises  directly  from  the  primitive  belly-stalk, 
which  was  shown  in  the  description  of  vesicles  10  and  18  to  con- 
sist of  paired  flat  bands  of  mesoderm  uniting  the  posterior  end 
of  the  embryo  to  the  margin  of  the  Trager  or  primitive  placenta. 
That  the  mesodermal  allantois  contributes  some  tissue  to  the  defi- 
nitive umbilicus  has  already  been  intimated,  but  at  no  time  do 
allantoic  blood  vessels  function.  The  placental  circulation  is 
carried  on  exclusively  by  the  umbilical  vessels,  paired  arteries  and 
veins.  Each  artery  arises  along  the  inner  margin  of  a  belly-stalk 
band,  while  each  vein  forms  in  the  scroll-like  outer  margin.  In 
later  stages  the  two  bands  fuse  at  a  short  distance  from  the  vesicle 


Development  of  the  Nine-Banded  Armadillo.  397 

and  continue  to  the  body  of  the  embryo  as  a  single  somewhat 
flattened  cord.  The  forked  connection  between  the  cord  and  the 
vesicle  is  maintained  as  a  characteristic  feature  of  the  placenta- 
tion.  In  the  definitive  condition  the  umbilicus  measures  from  18 
to  20  cm.  in  length  and  about  1  cm.  in  greatest  diameter.  The 
veins  are  longer  than  the  arteries  and  take  an  open  spiral  course 
along  the  flattened  edges  of  the  cord. 

VIII.     PAIRING  OF  THE  EMBRYOS 

In  our  preliminary  paper  attention  was  called,  in  treating  of  the 
nearly  complete  identity  of  the  four  embryos,  to  indications  of 
a  still  closer  resemblance  between  the  individuals  of  the  right 
and  left  hand  pairs.  In  attempting  to  derive  the  four  embryos 
from  the  blastomeres  of  the  four-cell  stage  the  following  suggestion 
was  offered:  "This  possible  interpretation  receives  a  striking 
confirmation  in  the  fact  that  the  four  embryos  can  be  arranged 
into  two  pairs,  the  individuals  of  which  approach  almost  complete 
identity;  and  these  identicals  are  not  only  adjacent  to  each  other 
but  are  also  attached  to  placental  discs  that  are  closely  united. 
If  all  four  embryos  are  derived  from  a  single  egg,  this  is  exactly 
what  we  should  expect  to  find;  for  surely  the  individuals  derived 
from  one  of  the  blastomeres  of  the  two-cell  stage  ought  to  be 
more  nearly  similar  to  each  other  than  to  the  individuals  of  the 
other  blastomere." 

The  subsequent  acquisition  of  a  large  amount  of  additional 
data  has  served  only  to  strengthen  our  conviction  concerning  this 
strong  tendency  toward  pairing  among  the  four  embryos:  a 
tendency  that  expresses  itself  in  the  method  of  separation  of  the 
embryos  from  the  common  amnion ;  in  the  fusion  of  the  four  discoid 
place'ntal  areas  into  two  double  lateral  discs ;  in  the  different  rates 
of  development  seen  in  the  embryos  of  a  single  vesicle;  and  in  the 
closer  resemblance,  as  a  rule,  between  the  paired  embryos  of 
one  double  placental  disc  than  between  the  embryos  in  general. 

The  forked  arrangement  of  the  amniotic  canals,  as  was  pointed 
out  in  connection  with  vesicles  10  and  18,  shows  that  the  embryos 
retreat  from  the  common  amnion  in  pairs  and  that  only  when  at 


398  H.  H.  Newman  and  J.  T.  Patterson. 

some  distance  from  the  latter  do  the  individuals  of  a  pair  sever 
their  intimate  connection  and  acquire  separate  amnia.  Subse- 
quently these  embryos  show  their  pairing  in  their  mode  of  attach- 
ment to  the  definitive  placental  discs,  embryos  I  and  II  being 
attached  to  the  right  hand  disc  and  III  and  IV  to  the  left. 

Fernandez  calls  attention  in  the  case  of  the  Mulita  to  the  exact 
identity  in  stage  of  development  among  the  embryos  of  a  set. 
That  this  is  not  always  fche  case  in  our  species  is  well  brought  out 
by  a  comparison  of  figs.  30  and  31,  two  embryos  from  vesicle  18. 

Fig.  30  represents  embryo  III,  and  IV  was  identical  with  it. 
Fig.  31  was  taken  from  embryo  II  but  would  serve  equally  well 
as  a  figure  of  I.  The  difference  in  degree  of  development  between 
the  two  pairs  is  well  marked  not  only  in  the  number  of  somites 
(5  in  III  and  IV  and  7  in  I  and  II),  but  in  the  conditions  in  the 
head  region  and  in  other  parts. 

It  is  not  likely  that  a  difference  in  rate  of  development  between 
the  two  pairs  is  of  common  occurrence,  but  the  clear  case  of  it 
just  presented  seems  worth  recording  not  only  on  account  of  its 
rarity  but  because  it  serves  to  emphasize  the  tendency  of  the  indivi- 
duals of  a  pair  to  be  alike,  but  somewhat  different  from  the  equally 
identical  opposite  pair. 

Although  of  very  common  occurrence  the  pairing  of  embryos  on 
the  basis  of  resemblances  in  the  total  number  of  scutes  in  the  nine 
bands  of  armor,  is  not  without  exception.  In  many  cases  the 
pairing  is  so  marked  as  to  be  startling,  as  for  example  in  one  case 
where  I  and  II  each  has  555  plates  and  III  and  IV  each  has  548 ; 
or  in  another  case  where  I  and  II  have  respectively  551  and  552 
and  III  and  IV  have  respectively  560  and'  559.  In  many  other 
cases  the  pairing  is  obvious  but  not  so  clean  cut. 

There  are  on  the  other  hand  two  cases  where  there  was  a  close 
resemblance  between  three  embryos,  but  one  was  strikingjy 
different,  as  for  example  where  II,  III,  IV  have  respectively 
544,  545,  543  and  I  has  549;  or  again  where  I,  II,  III  have 
respectively  562,  565,  564  and  IV  has  573.  Finally  two  cases 
occurred  in  which,  if  any  pairing  at  all  exists  it  appears  to  be 
between  I  and  III  and  between  II  and  IV,  as  for  example  where 
I  and  III  have  respectively  544  and  546  while  II  and  IV  have 
550  and  548. 


Development  of  the  Nine-Banded  Armadillo.  399 

On  the  whole  however,  in  spite  of  these  exceptions,  the  general 
rule  holds  good,  that  the  closest  resemblances  occurs  between 
paired  embryos. 

In  this  connection  it  should  be  mentioned  that  even  where 
there  is  exact  resemblance  between  the  individuals  of  a  pair  in 
the  total  number  of  scutes  in  the  nine  bands  of  armor,  there  is 
no  perfect  correspondence  with  respect  to  individual  rows.  The 
resemblance  in  total  numbers  of  scutes  is  however,  a  matter  of 
more  importance  than  the  exact  manner  of  their  arrangement 
into  rows,  which  is  a  secondary  process.  Each  primary  scute 
is  the  equivalent  of  a  well  defined  hair  group  atid  these  groups, 
as  can  be  seen  in  other  regions  of  the  body,  are  quite  definite  units, 
although  subject  to  more  or  less  shifting  before  reaching  their 
final  arrangement  into  rows.  In  a  subsequent  paper  we  expect  to 
make  a  special  study  of  variation  and  heredity  in  the  elements 
of  the  armor  and  shall  in  this  place  refrain  from  any  more  detailed 
reference  to  the  subject. 

Another  source  of  data,  however,  which  furnishes  striking  evi- 
dence of  pairing  is  seen  in  connection  with  a  fairly  common  ten- 
dency for  regional  fusion  of  adjacent  bands  of  armor,  or  for  the 
occurrence  of  interrupted  and  of  incomplete  bands  in  definite 
regions.  Such  atypical  conditions  occur  in  from  three  to  four 
per  cent  of  all  cases,  a  fact  that  we  have  established  from  an  exam- 
ination of  considerably  over  a  thousand  shells.  This  comparative 
rarity  of  occurrence,  while  it  renders  the  collection  of  data  on 
pairing  and  identity  difficult,  gives  to  such  data  an  added  value, 
in  that  chance  resemblances  are  very  unlikely  to  occur. 

Only  four  cases  of  strikingly  atypical  armor  arrangements  have 
so  far  been  discovered  in  the  collection  of  foetuses  now  in  our 
possession'.  In  one  case  in  embryos  I  and  II  there  occurred  a 
remarkably  atypical  scute  arrangement  in  the  first  band  of 
armor,  while  III  and  IV  were  quite  normal.  In  a  second  case 
I  and  II  showed  a  slight  fusion  between  the  first  two  rows  at  the 
right  hand  margin,  while  III  and  IV  showed  a  much  more  esten- 
sive  fusion  in  exactly  the  same  region.  The  pairing  in  this  case 
was  only  a  matter  of  degree  of  fusion,  but  there  was  a  decided  differ- 
ence in  extent  of  the  region  of  fusion  in  the  two  pairs.  In  a  third 


400  H.  H.  Newman  and  J.  T.  Patterson. 

case  III  and  IV  exhibit  almost  precisely  the  same  atypical  condi- 
tion, a  short  interruption  in  the  first  band  a  little  to  the  left  of  the 
median  line;  II  has  an  interruption  in  the  same  band,  involving 
considerably  more  than  half  of  the  total  length  of  the  band,  while 
I,  although  appearing  to  be  perfectly  normal,  seems  to  have  carried 
the  tendency  toward  the  suppression  of  a  band  to  the  extreme  in 
that  the  whole  band  is  lacking.  In  a  fourth  case  one  of  the  four 
embryos  shows  a  short  fusion  between  the  first  two  rows  on  the 
left  hand  side,  while  the  other  three  are  perfectly  normal. 

Three  out  of  four  cases,  then,  furnish  strong  evidence  of  pairing, 
while  the  fourth  case,  which  is  after  all  atypical  only  to  a  mini- 
mum extent,  affords  an  exception,  whose  weight  can  scarcely 
be  sufficient  to  discredit  the  evidence  of  the  other  cases. 

Although  the  pairing  of  embryos  is  not  always  perfectly  obvi- 
ous the  cumulative  evidence  in  favor  of  its  general  occurrence 
is  convincing  and  must  have  some  fundamental  significance,  an 
understanding  of  which  is  undoubtedly  closely  bound  up  with  the 
early  developmental  mechanics  as  we  shall  attempt  to  show. 

It  has  occurred  to  us  that  the  division  of  the  four-scalloped 
placental  band  into  right  and  left  lateral  discs  migh  t  be  dependent 
upon  the  fact  that  the  blood  supply  of  the  uterus  comes  from  the 
paired  ovarian  blood  vessels  that  enter  the  uterus  laterally.  It 
is  true  that  the  paired  embryos,  with  very  few  exceptions  are 
located  on  the  same  side  of  the  uterus,  but  that  the  pairing  is  in 
any  way  caasally  related  to  the  fact  of  their  location  near  the  en- 
trance of  a  single  maternal  blood  vessel  is  highly  improbable, 
because  the  maternal  blood  does  not  reach  the  embryos. 

It  has  also  been  suggested  that  the  close  resemblance  between 
the  individuals  of  a  pair  might  be  due  to  admixture  of  foetal  blood, 
but  we  have  demonstrated  by  the  use  of  colored  injections  that 
the  placental  area  of  each  embryo  is  sharply  circumscribed  and 
that  no  blood  passes  from  one  embryo  to  another.  A  common 
blood  environment  then  cannot  be  held  accountable  for  the  near 
approach  to  identity  seen  in  the  pairs.  Moreover  it  has  been 
shown  that  long  before  there  was  any  sign  of  the  definitive  placen- 
tation,  and  hence  before  there  was  any  circulation  of  blood,  pair- 
ing of  embryos  was  evident  in  the  relationship  of  the  amriiotic 


Development  of  the  Nine-Banded  Armadillo.          401 

connecting  canals  and  in  one  case,  in  the  degree  of  development 
of  the  embryos. 

These  observations  force  us  to  the  conviction  that  the  orienta- 
tion of  the  vesicle  in  the  uterus  and  the  pairing  of  the  embryos  are 
expressions  of  the  cleavage  polarity  and  symmetry  of  the  ovum. 
The  cell  products  of  the  first  two  blastomeres  would  occupy  the 
right  and  left  halves  of  the  early  blastocyst  and  the  daughter 
cells  derived  from  the  first  two  blastomeres  would  normally 
hold  their  relative  positions  as  quadrants  of  such  a  blastocyst,  so 
that,  although  it  may  not  be  possible  to  note  any  definite  demarka- 
tion  of  embryonic  primordia  until  a  much  later  stage,  they  may  be 
well  defined  from  the  first.  When  however  pairing  seems  to  exist 
between  diagonally  opposed  embryos  it  might  conceivably  be  due 
to  a  shifting  of  blastomeres  in  the  four-cell  stage,  which  could 
readily  occur  in  such  loose  cell  aggregates  as  prevail  in  early  mam- 
malian cleavage  stages.  A  shifting  upwards  of  two  diagonally 
placed  blastomeres  and  a  consequent  shifting  downward  of  the 
other  two  would  bring  about  a  recombination  of  blastomeres 
into  two  new  pairs  without  interfering  with  the  hereditary  ten- 
dencies of  the  individual  units.  Such  an  appeal  to  the  imagina- 
tion of  the  reader  would  scarcely  be  justified  were  it  not  the  logical 
outcome  of  a  failure  to  explain  the  conditions  on  any  other  basis. 
We  are  much  inclined,  in  spite  of  Fernandez'  failure  to  note  any 
indication  of  a  demarkation  of  separate  embryonic  areas  in  his 
earliest  vesicles,  to  believe  that  such  areas  exist  from  the  beginning 
and  express  themselves  as  separate  primordia  only  on  the  differ- 
entiation of  embryos.  This  view  is  in  direct  opposition  to  that  of 
Fernandez  who  holds  that  up  to  the  time  when  the  separate  em- 
bryos are  distinguishable,  the  vesicle  is  a  single  embryo. 

IX.     CONDITIONS    IN    VESICLES    CONTAINING   FIVE  FOETUSES 

Out  of  a  total  of  seventy  embryonic  vesicles  there  occurred 
three  in  which  there  were  five  foetuses.  In  all  of  these  the  sex 
could  be  determined  and,  curiously  enough,  they  were  all  males. 
Whether  or  not  this  condition  is  universal  could  not  be  determined. 
If  however  it  should  prove  that  all  five-embryo  sets  are  males  it 

JOURNAL   OP   MORPHOLOGY,   VOL.  21,    NO.  3. 


402  H.  H.  Newman  and  J.  T.  Patterson. 

would  mean  that  sex  is  determined  by  certain  conditions  in  the 
egg.  With  only  three  cases  in  hand  a  discussion  of  the  matter 
would  be  unprofitable. 

In  two  cases  out  of  three  it  was  possible  to  enumerate  the  scutes 
in  the  nine  bands  of  armor  and  on  that  basis  to  determine  the 
varying  degrees  of  resemblance  among  the  embryos. 

The  occurrence  of  five  embryos  involves  a  decided  asymmetry 
of  the  placental  and  amniotic  elements  and  an  atypical  arrange- 
ment of  the  embryos.  In  each  case  the  condition  of  two  main 
lateral  discs  was  maintained,  but  one  of  these  discs,  the  one  to 
which  three  embryos  were  attached,  was  considerably  larger  than 
the  other.  An  examination  of  the  larger  disc  shows  that  in  each 
case  it  is  composed  of  only  two,  not  three,  primary  discs.  One 
of  the  primary  discs,  on  the  side  where  three  embryos  are  attached, 
is  twice  the  normal  size  and  to  it  are  attached  in  symmetrical 
fashion  the  umbilical  cords  of  two  embryos.  Apparently  there  is 
no  regularity  about  the  position  of  the  double  disc.  In  one  case 
the  double  disc  is  ventral,  and  in  the  other  two  right  lateral  in 
position.  Believing  that  the  two  embryos  attached  to  a  single 
primary  disc  are  the  equivalent  of  one  typical  embryo,  we  shall 
give  them  the  same  number,  as  for  example,  I  and  I'. 

The  following  conditions  are  found  in  vesicle  91,  the  relative 
positions  of  the  embryos  being  indicated  in  the  diagram  of  the 
placenta,  represented  as  cut  open  along  the  narrow  dorsal  bridge 
and  laid  out  flat  (fig.  5) .  The  number  of  scutes  in  the  nine  bands 
of  armor  are  indicated  on  the  figure.  It  will  be  noted  that  there  is 
distinct  pairing  on  the  normal  side  of  the  vesicle,  between  em- 
bryos III  and  IV;  that  the  resemblance  between  the  two  embryos 
on  the  large  disc  (I  and  I')  is  equally  close;  but  that  there  is  a 
wide  difference  bewteen  these  two  embryos  and  the  single  embryo 
on  the  same  side  (no.  II). 

In  vesicle  108  somewhat  similar  conditions  exist,  but  the  vesi- 
cle is  laid  open  along  the  ventral  bridge  (fig.  6).  Embryos  II  and 
II',  having  a  common  primary  placental  disc,  are  identical  in  the 
number  of  scutes  but  widely  different  from  embryo  I,  which  is 
attached  to  the  other  primary  disc  on  the  same  side  of  the  vesicle. 
Embryos  III  and  IV  are  quite  different  from  those  on  the  other 
side,  but  are  fairly  similar  to  each  other. 


Development  of  the  Nine-Banded  Armadillo.  403 


6 

FIG.  5.  Diagram  of  the  placenta  of  vesicle  no.  91,  showing  the  placentation  and 
the  numbers  of  scutes  in  the  nine  bands  of  each  embryo.  Cut  open  along  the  dor- 
sal notch. 

• 

FIG.  6.     The  same  scheme  for  vesicle  108.    Cut  open  along  ventral  notch. 


404  H.  H.  Newman  and  J.  T.  Patterson. 

In  the  case  of  the  third  five-embryo  vesicle  a  satisfactory  enum- 
eration of  the  scutes  was  .not  found  possible,  but  the  position  of 
he  large  disc  was  the  same  as  in  108. 

In  all  three  cases  the  amnia  of  the  three  embryos  occurring  on 
the  same  side  are  irregularly  arranged.  Instead  of  occupying 
whole  quadrants  of  the  subspherical  vesicle  the  amnion  of  one  or 
more  embryos  is  forced  away  from  one  end  and  crowded  past  the 
opposite  end,  thus  causing  the  amniotic  partitions  to  run  diago- 
nally across  the  placental  discs  instead  of  taking  a  meridional 
course  from  pole  to  pole  as  in  typical  cases.  The  relative  positions 
of  the  embryos  is  of  course  correspondingly  irregular  so  that  one 
is  immediately  struck  by  it  when  the  vesicle  is  first  exposed  to 
view. 

The  high  degree  of  mal-adjustment  seen  in  these  vesicles  would 
seem  to  indicate  that  the  occurrence  of  more  than  four  embryos 
is  the  expression  of  a  coenogenetic  tendency  to  carry  polyembryony 
a  step  farther  by  a  doubling  of  the  present  typical  number  of 
embryos.  In  the  Mulita  this  condition  has  been  attained  and  there 
exists  a  strong  tendency  to  double  again,  as  seen  in  the  frequency 
of  vesicles  containing  nine  or  more  embryos.  It  appears  probable 
to  us  in  view  of  the  occurrence  of  one  case  of  twins  in  our  collection, 
that  in  T.  novemcinctum  specific  polyembryony  had  its  origin  in 
the  acquisition  of  a  habit  of  producing  identical  twins  in  a  fashion 
similar  to  that  seen  in  other  mammals,  that  the  inversion  of  germ 
layers  made  it  easy  for  this  tendency  to  express  itself  still  more 
fully  in  the  habitual  production  of  four  embryos.  The  production 
of  more  than  four  embryos  in  our  species  seems  to  involve  so 
great  a  disturbance  of  a  very  accurate  adjustment  of  embryos 
and  embryonic  membranes  that  it  seems  highly  improbable  that 
a  larger  number  of  embryos  will  ever  become  typical. 

It  would  be  interesting  to  find  out  whether  there  is  in  T.  hybri- 
dum  any  tedency  of  the  embryos  to  arrange  themselves  into  two 
groups  corresponding  to  the  right  and  left  sides  of  the  vesicle.  A 
study  of  Fernandez'  photographs  (figs.  1  and  2)  would  seem  to  in- 
dicate that  such  is  the  case.  It  is  hoped  that  this  matter  will 
receive  some  attention  and  that  the  degree  of  resemblances 
among  the  embryos  of  the  various  sets  will  be  determined. 


Development  of  the  Nine-Banded  Armadillo.          405 
X.    THE  QUESTION  OF  IDENTITY  OF  EMBRYOS 

In  the  case  of  identical  or  monochorial  twins  the  question  of 
close  resemblance  has  been  much  discussed  and  the  impression 
seems  to  prevail  that  the  individuals  of  a  pair  show  such  marked 
similarity  in  their  finer  details  of  structure  as  to  be  practically 
identical. 

In  our  earlier  contribution  to  this  subject  we  were  inclined  to 
look  for  the  resemblances  between  the  embryos  of  a  litter  and  to 
understimate  the  value  of  the  points  of  difference.  Now  however 
that  we  feel  that  the  question  of  specific  polyembryony  has  been 
established,  the  differences  among  embryos  interest  us  more 
than  the  resemblances,  because  they  indicate  a  rather  marked 
degree  of  versatility  in  the  hereditary  possibilities  of  a  single 
fertilized  germ  cell. 

The  only  point  of  unfailing  identity  among  the  individuals  of 
a  litter  is  that  of  sex.  In  38  cases  where  the  sex  was  definitely 
determined  there  was  no  exception  to  the  rule  that  all  embryos 
in  a  vesicle  are  of  the  same  sex. 

So  far  as  dimensional  differences  go  there  is  again  practical  iden- 
tity, although  in  a  few  cases»  there  seemed  to  be  a  slight  difference 
in  the  size  of  the  two  pairs.  In  comparing  one  individual  with 
another  we  were  forced  to  admit  that  they  differed  only  in  the 
minutest  details,  such  as  the  number  of  scutes  in  the  armor.  A 
comparison  on  this  basis  is  just  about  as  searching  as  would  be  a 
comparison  of  the  number  of  feathers  in  a  given  feather  tract  of 
two  birds,  or  of  the  hairs  in  a  given  hair  area  of  two  mammals. 
We  have  for  the  present  limited  our  comparison  to  the  total  num- 
ber of  large  scutes  (with  corresponding  underlying  bony  plates), 
in  the  nine  moveable  bands  of  armor.  The  extreme  range  of 
variability  in  the  total  number  of  these  plates  (in  all  of  the  indi- 
viduals so  far  examined)  is  rather  wide,  running  from  511  to  620, 
a  range  of  109.  In  a  number  of  cases  the  individuals  of  a  litter 
exhibit  a  range  of  only  five  or  six  scutes,  but  as  a  rule  the  range 
is  wider,  averaging  in  all  cases  studied  twelve,  or  less  than  one- 
ninth  of  the  total  range  of  our  sample  of  the  species.  Whether 
or  not  this  represents  a  closer  esemblance  than  exists  between 


406  H.  H.  Newman  and  J.  T.  Patterson. 

the  individuals  in  a  litter  of  rats  or  other  mammals  cannot  •  at 
present  be  determined. 

Although  the  difference  between  the  two  pairs  of  a  litter  may 
on  the  average  be  rather  marked,  that  between  the  individuals 
of  a  pair  seldom  exceeds  three  scutes  and  averages  in  all  cases 
observed  less  than  three,  while  cases  of  absolute  identity  in  the 
total  number  of  scutes  is  of  frequent  occurrence. 

It  will  be  remembered  also  that  in  our  discussion  of  pairing  a 
considerable  mass  of  evidence  was  adduced  to  show  that  even  in 
atypical  scute  arrangements  a  high  degree  of  identity  existed 
between  pairs,  while  in  most  cases  the  pairs  differed  greatly  from 
each  other.  All  of  these  observations  go  to  show  that  the  identity 
between  the  individuals  of  a  pair  is  a  very  real  thing  but  that  the 
there  is  nothing  approaching  true  identity  between  the  pairs. 
The  condition  may  well  be  described  as  a  case  of  double  identical 
twins. 

XI.    SPECIFIC   POLYEMBRYONY  AND   THE   DETERMINATION 

OF   SEX 

The  first  clue  to  the  existence  of  polyembryony  in  the  armadillos 
was  furnished  by  the  discovery  that  all  of  the  individuals  of  a  litter 
are  of  the  same  sex.  This  together  with  his  observation  of  a  com- 
mon chorion,  led  von  Jhering  to  surmise  that  all  of  the  embryos 
of  a  vesicle  arise  from  a  single  fertilized  egg.  That  this  flash 
of  insight  foreshadowed  the  discovery  of  a  truth  has  been  suffi- 
ciently demonstrated,  we  believe,  by  Fernandez  for  Tatu  hybri- 
dum  and  by  us  for  T.  novemcinctum. 

Identity  of  sex  then  is  in  some  way  closely  bound  up  with  the 
phenomenon  of  polyembryony.  Presumably  all  of  the  individuals 
of  a  litter  are  of  the  same  sex  because  they  have  been  derived 
from  a  single  fertilized  ovum;  but  this  presumption  involves  the 
corollary  that  sex  is  determined  in  the  germ  before  any  demarka- 
tion  of  embryonic  rudiments  has  occurred.  The  only  alternative 
is  that  similarity  of  environmental  conditions  during  the  devel- 
opmental period  has  the  effect  of  producing  offspring  all  of  the 
same  sex,  an  alternative  with  no  factual  basis,  as  is  shown  by  the 


Development  of  the  Nine-Banded  Armadillo.          407 

following  observations :  that  at  a  very  early  period  each  embryo 
is  surrounded  by  its  own  amnion;  that  a  little  later  each  draws 
maternal  nutriment  from  a  separate  area  of  the  uterine  wall;  and 
that  there  is  no  admixture  of  foetal  blood.  We  are  therefore 
driven  to  the  conclusion  that  sex  is  determined  before  there 
occurs  any  splitting  of  the  single  germ  into  separate  embryonic 
primordia. 

Opinions  differ  as  to  the  exact  period  at  which  this  splitting 
takes  place.  Fernandez  maintains,  on  the  basis  of  his  studies  of 
the  early  blastocyst  of  the  mulita,  that  there  is  no  trace  of  poly- 
embryony  until  after  the  two  primary  germ  layers  have  been 
laid  down.  What  he  probably  means  is  that  previous  to  this  time 
there  is  no  visible  demarcation  of  the  germ  layers  into  isolated 
blastodermic  areas.  That  the  real  separation  of  embryonic  rudi- 
ments occurs  at  a  much  earlier  period,  even  during  the  early  cleav- 
age stages  (in  our  species  at  the  four-cell  stage),  seems  probable 
in  view  of  the  discovery  of  pairing  among  the  embryos,  a  phenome- 
non for  which  no  other  explanation  offers  itself;  and  by  the  obser- 
vations of  Marchal,  ('04),  and  Silvestri  ('06),  on  the  parasitic 
hymenoptera,  where  each  embryo  in  a  set  takes  its  rise  from  a 
single  cell  of  a  rather  advanced  cleavage  stage. 

It  seems  highly  probable  then  that  the  tissues  involved  in  each 
of  the  four  quadrants  of  an  embryonic  vesicle,  whether  or  not 
they  may  show  a  demarcation,  do  really  arise  as  the  lineal  descend- 
ants of  one  of  the  first  four  blastomeres.  In  this  sense  the  four 
embryos  are  delimited  at  the  four  cell  stage.  It  is  hardly  to  be  ex- 
pected that  any  demarcation  would  be  visible  before  the  beginning 
of  the  period  when  the  separate  embryonic  shields  are  differen- 
tiated. 

The  question  as  to  the  exact  period  of  separation  of  the  several 
embryonic  rudiments  is  one  that  cannot  at  present  be  definitely 
settled.  Even  if  one  should  be  fortunate  enough  to  obtain  the 
early  cleavage  stages  it  is  improbable  that  he  would  be  able  to 
observe  any  essential  departure  from  the  usual  plan  of  mammalian 
cleavage,  for  a  blastomere  of  the  four  cell  stage  would  have  the 
same  appearance  whether  it  were  destined  to  produce  a  whole 
or  only  a  quarter  of  an  embryo. 


408  H.  H.  Newman  and  J.  T.  Patterson. 

It  seems  probable  from  our  studies  of  the  ovaries  that  the  ten- 
dency to  polyembryony  is  inherent  in  the  unfertilized  egg,  which 
is  the  seat  of  a  developmental  vigor  somewhat  more  intense  than 
that  exhibited  in  the  ova  of  other  mammals.  This  extra  expresses 
itself  sometimes  by  parthenogenetic  divisions  and  at  other  times 
in  the  formation  of  fairly  regular  morulae  within  the  confines  of 
the  Graafian  follicles.  That  polyembryony  is  simply  a  more  nor- 
mal expression  of  the  same  superabundant  energy  in  the  female 
germ  cells  seems  highly  probable,  and  we  would  offer  this  as  a 
tentative  explanation  of  the  physiology  of  polyembryony,  pending 
an  exhaustive  study  of  a  large  collection  of  ovaries. 

Taking  it  for  granted  then  that  sex  is  determined  in  the  undi- 
vided oosperm,  the  question  naturally  arises  as  to  which  of  the 
two  germinal  elements  is  the  sex  determiner.  Cytological  exam- 
ination of  the  ovaries  reveals  no  dimorphism  of  the  ova.  They  all 
have  32  chromosomes  and  are  equally  alike  in  other  respects. 
The  possibility  that  sex  might  depend  on  which  of  the  two  ovaries 
produced  the  egg  that  became  fertilized  as  suggested  by  the  work 
of  Dawson  ('09) .  This  writer  maintains  on  observational  grounds 
that  in  the  human  being  the  male  producing  ova  come  from  the 
right  and  the  female  producing  ova  from  the  left  ovary.  The  cor- 
pus luteum  served  to  indicate  which  ovary  functioned  in  any  given 
pregnancy.  In  the  armadillo  we  have  an  exceptional  opportunity 
to  put  Dawson's  theory  to  a  test,  for  the  corpus  luteum  of  this 
species  is  a  very  prominent  feature  of  the  ovary  that  has  func- 
tioned. A  study  of  our  data  reveals  the  fact  that  the  corpus 
luteum  is  found  with  almost  equal  frequency  in  right  and  left  ova- 
ries, which  coincides  with  the  exact  equality  of  male  and  female 
litters.  Unfortunately  for  the  theory,  however,  there  is  no  cor- 
relation between  the  sex  of  the  embryos  and  the  dextrality  or 
sinistrality  of  the  functional  ovary.  Out  of  twenty ^cases  in  which 
the  right  ovary  contained  the  corpus  luteum,  the  sex  of  the  em- 
bryos was  male  in  seven  and  female  in  thirteen;  while  out  of 
thirteen  cases  in  which  the  left  ovary  held  the  corpus  luteum, 
the  sex  was  male  eight  times  and  female  five.  Evidently  then 
the  position  of  the  functional  ovary  has  no  determining  influence 
on  sex. 


Development  of  the  Nine-Banded  Armadillo.  409 

There  is  on  the  other  hand  excellent  evidence  that  the  male  cell 
may  act  as  a  sex  determiner.  Studies  of  the  spermatogenesis 
of  our  species  show  that  the  spermatogonial  number  of  chromo- 
somes is  in  all  probability  31,  one  less  than  the  oogonial.  There 
is  moreover  in  the  reduction  division  a  very  definite  and  obvious 
odd  chromosome,  which  precedes  the  other  chromosomes  to  the 
pole  of  the  spindle  and  serves  to  institute  a  dimorphism  of  the 
spermatids.  That  the  odd  chromosome  is  concerned  with  the 
determination  of  sex  is  as  probable  for  the  armadillo  as  for  the 
insects  and  other  forms  in  which  it  has  been  described.  Both 
rest  on  the  same  observations.  Since  it  is  our  intention  to  make 
a  detailed  study  of  the  cytology  of  the  germ  cells  in  this  species, 
it  must  suffice  for  the  present  to  have  indicated  the  sort  of 
external,  evidence  of  polyembryony  and  of  sex  determination  we 
have  at  our  command. 

The  discovery  of  so  clear  a  case  of  an  accessory  chromosome 
in  a  mammal  is  in  itself  worthy  of  mention,  since  it  brings  us  a 
few  steps  nearer  to  the  discovery  of  the  physiology  of  sex  deter- 
mination in  man.  In  addition  to  the  intrinsic  value  of  this  dis- 
covery, however,  we  are  afforded  another  strong  proof  of  specific 
polyembryony,  in  that  it  is  highly  improbable,  on  the  basis  of 
the  origin  of  the  embryos  of  a  vesicle  from  several  fertilized  eggs 
that  each  of  these  eggs  would  be  fertilized  by  the  same  kind  of 
•spermatozoon.  Such  a  possibility  could  be  realized  only  through 
the  instrumentality  of  selective  fertilization,  the  occurrence  of 
of  which  has  never  been  successfully  demonstrated. 

XII.     SUMMARY   OF   EVIDENCE   FOR   SPECIFIC   POLYEMBRYONY 

1.  The  uterus  is  simple,  resembling  that  of  the  primates,  which 
give  birth  typically  to  one  offspring  at  a  time. 

2.  There  is  never  more  than  one  large  corpus  luteum  in  the 
ovaries  of  a  pregnant  female. 

3.  In  over  90  per  cent  of  vesicles  the  number  of  normal  embryos 
is  four,  a  number  that  suggests  their  origin  from  the  blastomeres 
of  the  four-cell  stage.    It  is  also  unlikely  that  this  number  of  ova 
would  so  often  be  given  off  at  the  same  time. 


410  H.  H.  Newman  and  J.  T.  Patterson. 

4.  The  fact  that  all  of  the  embryos  of  a  set  are  invariably  of  the 
same  sex  strongly  suggests  their  origin  from  a  single  fertilized  egg. 

5.  The  definite  orientation  of  the  embryos  in  the  vesicle,  and 
of  the  vesicle  in  the  uterus,  precludes  the  possibility  of  their  origin 
from  several  eggs,  even  though  these  might  conceivably  be  simul- 
taneously given  off  from  the  ovary. 

6.  The  inversion  of  germ  layers  presents  a  condition  in  both 
Tatu  hybridum  and  in  T.  novemcinctum,  which  could  not  be  at- 
tained by  the  union  of  several  eggs  to  form  a  single  vesicle.    This 
is  the  strongest  piece  of  evidence  for  specific  polyembryony  that 
has  been  advanced,  and,  to  our  minds,  is  practically  conclusive. 

7 .  The  Trager  or  primitive  placenta,  common  to  all  four  embryos, 
is  the  morphological  equivalent  of  that  seen  in  the  monembryonic 
vesicles  of  certain  rodents. 

8.  The  overgrowing  fringe  of  arborescent  villi  seen  in  middle 
stages  of  gestation  reminds  one  strongly  of  the  cricoid  placenta 
seen  in  the  monembryonic  vesicle  of  the  six-banded  armadillo, 
figured  by  Chapman. 

9.  The  existence  of  partial  or  rudimentary  embryos  is  evidence 
against  the  idea  that  the  several  embryos  have  been  derived  from 
separate  eggs,  for  it  is  difficult  to  understand  why  some  should 
develop  perfectly,  while  others,  under  the  same  environmental 
conditions,  should  have  so  little  success. 

10.  The  pairing  of  embryos  points  to  the  origin  of  each  pair 
from  one  of  the  first  two  blastomeres. 

11.  The  presence  of  an  accessory  chromosome  in  the  male  germ 
cells  suggests  that  the  spermatozoon  is  the  sex  determiner.    On 
this  basis  the  fertilization  of  several  eggs  always  by  the  same  kind 
of  spermatozoa  seems  highly  improbable. 


Development  of  the  Nine-Banded  Armadillo.  411 

BIBLIOGRAPHY 

BAILEY,  Vernon.     Biological  Survey  of  Texas.    North  Amer.  Fauna,  no.  25. 

1905. 
BEDDARD,  F.  E.     Mammalia.    Cambridge  Natural  History,  vol.  10. 

1902. 
CHAPMAN,  H.  C.  Observations  upon  the  placenta  and  youngof  Dasypus  sexcinctus 

1901.  Proc.  Acad.  Nat.  Sci.    Philadelphia,  pp.  1-4. 

CUENOT,  L.     L'ovaire  des  Tatous  et  1'origine  des  jinneaux.     C.  R.  Soc.  Biolog- 

1903.          T.  60,  pp.  1391-1392. 
DAWSON,  E.  R.     The  causation  of  sex.    London,  H.  K.  Lewis  Co.    pp.  1-190. 

1909. 
DUGES.     Annales  des  Sciences  Naturelles,  Sixieme  Ser.    Zool.  9.  p.l. 

1879. 
FERNANDEZ,  MIGUEL.     Beitrage  zur  Embryologie  der  Giirteltiere,  1.    Zur  Keim- 

1909.          Matter-inversion  und  spezifischen  Polyembryonie  der  Mulita  (Ta- 

tusia  hybrida  Desm.).    Morpholog.  Jahrb.  Bd.  39,  pp.  302-333. 
HUBRECHT,  A.  A.  W.     Early  ontogenetic  phenomena  in  mammals  and  their  bear- 

1908.  ing  on  our  interpretation  of  phylogeny  of  the  vertebrates.  Q.  J.  M. 
5.,  vol.  53,  pp.  1-181. 

JHERING,  H.  von.     Ueber  die  Fortpflanzung  der  Giirteltiere.    Sitzungsberichte  der 

1885.  konigl.  preuss.  Akademie  der  Wissenchaften.    Heft  47,  S.  105. 

1886.  Ueber   Generationswechsel    bei    Saugetieren.     Archiv  /.   Anatomie 

und  Physiologie,  Physik.  Abteilung.,  s.  442-450. 

Nachtrag    zur   Entwicklung   von    Praopus.     Ebenda.     s.    541-542. 
JENKINSON,  J.  W.     A  reinvestigation  of  the  early  stages  of  the  development  of 

1900.          the  mouse.    Q.  J.  M.  S.,  vol.  43,  pp.  61-82. 
KOLLIKER,  A.     Lehrbuch  der  Entwicklungsgeschichte  des  Menschen.    p.  362. 

1876. 

LANE,  H.  H.     Placentation  of  an  armadillo.    Science,  N.  S.  vol.  29,  p.  715. 
1909. 

1909 .  Some  observations  on  the  habits  and  placentation  of  Tatu  Novem- 

cinctum.    Bull.  State  Univ.  of  Oklahoma,  no.  1.     pp.  1-li. 
1909.       A   suggested    classification  of   edentates,    idem,    no.  2.  pp.    21-27. 
MARSCHAL,  P.     Recherches  sur  la  biologic  et  le  developpement  des  Hynenopteres 
1904.          parasites.      I.    La    polyembryonie    specifique    ou    germinogonie. 

Arch.  Zool.  Exper.,  Series  4,  vol.  2,  pp.  257-335. 
MELLISSINOS,  KONST.    Die  Entwicklung  des  Eies  der  Maus.     Archiv  /.  mikr. 

1907.          Anat.  Bd.  70  pp.  587-628. 

MILNE-EDWARDS,   A.     Sur  la  conformation    des  placenta  chez  le  Tamandua, 
1872.  Ann.  des  Sci.  Nat.,  15. 

1878.       Recherches  sur  les  enveloppes  fcetales  du    Tatou  a  neuf    bandes. 

Ann.  Nat.,  Ser.  6.    Zool.  T.  8. 

NEWMAN  H.  H.  AND  PATTERSON,  J.  T.    A  case  of  normal  identical  quadruplets 
1909.          in  the  nine-banded  armadillo,  and  its  bearing  on  the  problems  of 
identical  twins  and  of  sex  determination.     Biol.  Bull.,  vol.  17, 
no.  3,  pp.  181-187. 


412 


H.  H.  Newman  and  J.  T.  Patterson. 


ROBINSON,  ARTHUR.     Observations  upon  the  development  of  the  segmentation 

1892.          cavity,  the  artfhenteron,  the  geiminal  layers,  and  the  amnion  in 

mammals.     Q.  J.  M.  S.,  vol.  43,  pp.  369-456. 
ROSNER,  M.  A.     Sur  la  genese  de  la  grossesse  gemellaire  monochoriale.     Bull. 

1901.          Acad.  Sc.  de  Cracovie. 
SELENKA,   EMIL.     Die   Blatterumkehrung  im  Ei   der  Nagethiere.     Wiesbaden, 

1884.          pp.  67-99. 
SILVESTRI,  FILIPPO.     Contribuzioni  alia  conoscenza  biologica  degli  Imenotteri 

1906.          parassiti.   I.  Annali  R.  Scuola  Sup.  d"  Agricoltura.     Portici.  vol. 
6.  15  Gennaio,    1906. 


REFERENCE   LETTERS 


a. a.,   amniotic  attachment  to  wall  of 

vesicle. 
al.,  allantois. 

al.en.,  allantoic  entoderm. 
al.ms.,  allantoic  mesoderm. 
am.,  amnion. 
am.c.,  amniotic  cavity. 
am.c.c.,  amniotic  connecting  canal. 
a.v.,  aborescent  villi. 
b.b.,  belly-stalk  bands. 
b.c.,  blood  cords. 
b.s.,  belly-stalk. 
b.v.,  blood  vessel. 
c.,  cervix  of  uterus. 
c.a.,  clear  area  of  Trager. 
c.am.c.,  canal  of  the  common  amnion. 
c.e.,  canal  enlargement. 
c.L,  corpus  luteum. 
co.}  coelome. 
d.b.,  dorsal  bridge. 
d.n.,  dorsal  notch. 
ec.,  entoderm. 
en.,  entoderm. 
e.v.,  extra  chorionic  vesicle. 
ex.c.,  extra  embryonic  body  cavity. 
f.g.,  fore-gut. 

f.n.t.,  floor  of  the  neural  tube. 
f.t.t  Fallopian  tube. 
f.u.,  fundus  end  of  uterus. 
/.».,  flattened  villi  of  Trager. 
h.f.,  head  fold. 
h.ms.,  head  mesoderm. 
h.p.,  head  process. 
i.,  infundibulum  of  the  Fallopian  tube. 


i.L,  intestinal  loop. 
l.s.,  lymph  sinus. 
ms.,  mesoderm. 

ms.co.,  mesodermal  connection. 
m.p.,  medullary  plate. 
n.ch.,  notochord. 
n.g.,  neural  groove. 
n.l.L,  notch  of  the  left  lateral  lobe. 
o.,  ovary. 

p. am.,  posterior  amniotic  process. 
p. am.c.,  posterior  amniotic  cavity. 
p.p.h.,  protochordal  plate  of  Hubrecht. 
p.p.,  primitive  pit. 
p.r.,  placental  ring. 
p.s.,  primitive  streak, 
s.,  somite. 

s.am.c.c.,  supernumerary  connecting  can- 
al of  amnion. 
s.t.,  sinus  terminalis. 
s.v.,  scale-like  villi. 
t.m.p.,  tip  of  the  medullary  plate. 
tr.,  Trager. 
tr.c.,  Trager  cavity. 
tr.e.,  Trager  epithelium. 
tr.k.,  Trager  knots. 
u.m.,  uterine  mucosa. 
v.,  villi. 
vg.,  vagina. 
y.s.j  yolk-sac. 
y.s.en.,  yolk-sac  entoderm. 
y.s.w.,  yolk-sac  wall. 
I,  II,  III,  and  IV,  refer  respectively  to 
the   ventral,  right   lateral,  dorsal,  and 
left  lateral  embryos. 


Development  of  the  Nine-Banded  Armadillo.          413 


c.  i     o 


-*5**' C 


—  vg 


he. 


8 


FIG.  7.  The  genitalia  of  an  adult  virgin  female  as  seen  from  the  dorsal  aspect. 
b.L,  broad  ligament;  c.,  cervix  of  uterus;  c.L,  coprus  luteum  in  left  ovary;  f.u. 
fundus  end  of  uterus ;/.<.,  fallopian  tube;  i.,  infundibulum;  o.,  ovary.  X  3. 

FIG.  8.  Portion  of  the  yoik-sac  wall  in  the  region  of  the  area  vasculosa  (see  fig. 
15).  It  shows  three  blood  cords  in  section.  These  are  made  up  of  a  central  core  of 
solidly  packed  cells,  b.c.,  which  are  surrounded  by  the  mesodermal  epithelium,  ms. 
X  215. 

FJG.  9.  Cross  section  of  the  Trager  of  our  youngest  vesicle  (fig.  12),  showing 
three  adjacent  Trager  cords  or  knots  (tr.k) ;  tr.e.,  Trager  epithelium.  X  265. 


414 


H.  H.  Newman  and  J.  T.  Patterson. 


11 


FIG.  10.  Cross  section  of  scale-like  villi,  v.,  of  the  vesicle  in  fig.  14.  The  Trager 
knots  are  still  covered  with  a  thin  epithelium.  The  epithelium  of  the  villi  has 
become  a  syncytium.  The  mesoderm  has  proliferated  cells  which  have  invaded 
the  villi,  but  as  yet  blood  formation  has  not  taken  place.  X  265. 

FIG.  11.  The  tip  of  a  villus  from  a  more  advanced  stage,  showing,  in  addition  to 
the  features  described  in  preceding. figure,  the  well  developed  blood  vessels,  b.v. 
X  265. 


Development  of  the  Nine-Banded  Armadillo.  415 


--  c.am 


12 


FIG.  12.  A  detailed  drawing  of  vesicle  no.  10  as  seen  from  the  ventral  side  as  a 
semi-transparent  object.  The  embryos  in  white  (I  and  IV)  are  on  the  upper  side 
of  the  vesicle,  and  since  there  is  an  inversion  of  germ  layers,  these  are  seen  from 
their  ventral  aspects.  Embryos  II  and  III  are  shaded,  and  lie  on  the  far  side  of  the 
vesicle.  For  a  fuller  description  see  text.  X  9. 


416 


H.  H.  Newman  and  J.  T.  Patterson. 


anrac. 


--  am 


13 


JIIG.  13.  A  detailed  drawing  of  embryo  I  (fig.  12) as  seen  from  the  dorsal  aspect, 
that  is,  as  viewed  from  the  inside  of  the  vesicle,  am.,  amnion;  a.mc.c.,  connecting 
canals  of  the  amnion;  p.am.,  posterior  amniotic  process;  b.s.,  belly-stalk;  tr., 
Trager.  X  25. 


Development  of  the  Nine-Banded  Armadillo.          417 


14 


FIG.  14.  Ventral  view  of  vesicle  No.  18,  seen  as  a  semitransparent  object.  The 
Trager  is  covered  with  scale  like  villi,  which  overlap  the  lower  margin  of  the  yolk- 
sac.  This  vesicle  should  be  compared  with  that  shown  in  fig.  12,  in  which  the  let- 
tering is  the  same.  X  5. 


JOURNAL   OF   MORPHOLOGf,    VOL.  21      NO.    3. 


418 


H.  H.  Newman  and  J.  T.  Patterson. 


amxic. 


p.am. 


15 

FIG.  15.  A  detailed  drawing  of  embryo  I  (fig.  14)  as  seen  from  the  dorsal  side.  A 
photograph  of  this  embryo  is  shown  in  fig.  31.  al.,  allantois;  am.  ex.,  connecting 
canal  of  amnion;  6.6.,  belly-stalk  band,  note  that  the  band  is  much  more  distinct 
on  the  left  side  than  on  the  right;  p.s.,  primitive  streak;  s.v.,  scale-like  villi;  tr., 
Trager  region,  which  shows  the  villi  as  seen  from  their  under  sides.  For  a  fuller 
description  see  text.  X  21. 


Development  of  the  Nine-Banded  Armadillo.          419 


NOTE — Figs.  16-23  represent  a  series  of  transverse  sections  taken  through  various 
regions  of  an  embryo  from  the  same  vesicle  as  that  shown  in  fig.  13. 

FIG.  16.  A  section  taken  through  the  anterior  end  of  the  medullary  plate.  The 
most  important  feature  of  this  section  is  the  thickening  of  the  entoderm  to  form 
the  "protochordal  plate"  of  Hubrecht,  p.p.h.  X  130. 

FIG.  17.  A  section  taken  through  the  medullary  plates  at  a  point  lying  half  way 
between  the  fore  end  of  the  head  process  and  the  anterior  tip  of  the  embryo.  The 
entoderm  is  distinct  from  the  mesoderm,  which  is  scarcely  more  than  one  cell  thick. 
X  130 


420 


H.  H.  Newman  and  J.  T.  Patterson. 


FIG.  18.  A  section  taken  through  the  middle  of  the  head  process.  In  this  region 
the  entoderm  is  very  intimately  associated  with  the  mesoderm,  especially  in  the 
central  part  of  the  section.  X  130. 

FIG.  19.  A  section  taken  through  the  primitive  pit.  It  shows  the  primitive 
streak  proliferating  mesoderm  in  the  characteristic  manner.  X  130. 


Development  of  the  Nine-Banded  Armadillo.          421 


FIG.  20.  A  section  taken  through  the  connecting  canal,  which  is  seen  to  be  com- 
posed of  two  layers,  ectoderm  on  the  inside  and  mesoderm  on  the  outside,  and  is 
loosely  connected  with  the  mesoderm  of  the  yolk-sac  wall.  X  143. 

FIG.  21.  A  section  taken  through  the  tip  of  the  medullary  plate.  This  is  the  first 
section  that  shows  the  anterior  end  of  the  protochordal  plate  of  Hubrecht.  Note 
that  there  are  a  few  scattering  mesoderm  cells  (ms.)  that  have  wandered  in  between 
the  plate  and  the  ectoderm.  X  143. 

FIG.  22.  A  section  taken  through  the  belly-stalk  at  the  level  of  the  mouth  of  the 
allantois  (aZ.)-  The  cavity  of  the  posterior  amnotic  process  (p.am.c.)  does  not  cover 
more  than  one-half  the  width  of  the  section.  The  mesoderm  of  the  belly-stalk 
extends  laterally  to  form  wing-like  processes.  These  are  the  belly-stalk 
bands  (6.6.)  through  which  the  umbilical  blood  vessels  pass  to  the  Trager.  X  143. 


422 


H.  H.  Newman  and  J.  T.  Patterson. 


FIG.  23.  A  section  taken  through  the  belly-stalk  near  the  posterior  tip  of  the  al- 
lantoic  entoderm  (al.  en.}.  The  mesoderm  is  indistinctly  divided  into  two  por- 
tions: (1)  that  forming  the  belly-stalk  bands,  and  (2)  that  part  immediately  sur- 
rounding the  allantoic  tube — this  may  be  called  the  allantoic  mesoderm  (al.ms.}. 
The  belly  stalk  is  here  separated  from  the  wall  of  the  yolk-sac  by  a  space  (ex.c .), 
which  is  only  a  part  of  the  general  extra-embryonic  cavity.  X  143. 


Development  of  the  Nine  Banded  Armadillo. 


423 


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PLATE  I 

EXPLANATION    OF   FIGURES 

NOTE,  figs.  26-29  represent  a  series  of  transverse  sections  of  a  five-somite  embryo. 

26.  A  section  through  the  region  of  the  head-fold.  The  brain  vesicle  is  in  the 
process  of  formation,  and  the  neural  groove  (n.g.)  has  become  very  deep.  The  no- 
tochord  (n.ch.)  is  represented  by  a  row  of  cells,  and  to  each  side  of  it  the  entoderm 
is  bayed  to  form  the  pharyngeal  pouches  (ph.g.}.  X  68. 

.  27.  A  section  through  the  somite  region.  The  somite  shows  a  distinct  cavity, 
and  the  coelomic  cavity  is  forming.  The  entoderm  is  beginning  to  close  in  beneath 
the  notochord.  X  68. 

28.  A  section  through  the  proximal  part  of  the  allantoic  tube.    The  bands  of 
the  belly-stalk  have  become  much  folded,  and  contain  a  number  of  umbilical  blood 
vessels.    The  posterior  amniotic  process  has  become  reduced  to  a  very  small  tube. 
X  68. 

29.  A  section  through  the  posterior  mesodermal  connection  (ras.co.)   of  the 
belly-stalk.    The  Trager  shows  the  villi  in  the  process  of  formation.    X  30. 


DEVELOPMENT  OF  THE  NINE-BANDED  ARMADILLO. 
H.  H.  NEWMAN  AND  J.  T.  PATTERSON 


PLATE  I. 


26 


n.ch. 


en  a  1.  en.  alms. 


28 


29 


JOURNAL  OF  MORPHOLOGY,  VOL.  21,   NO.  3. 


PLATE  II 

EXPLANATION   OF   FIGURES 

30.  One  of  the  five  somite  embryos  (III)  of  vesicle  No.  18  (see  figs.  14  and  32) . 
Note  how  the  embryo  is  attached  to  the  Trager  by  means  of  the  belly-stalk  (6.s.). 
The  area  vasculosa,  like  that  of  the  chick,  does  not  extend  in  to  the  embryo,  but 
is.  separated  from  it  by  a  clear  space  which  corresponds  to  the  area  pellucida.    On 
the  right  is  seen  the  compound  sinus  terminalis  (s.t.)  lying  between  the  vascular 
areas  of  the  two  contiguous  embryos.    The  posterior  prolongation  of  the  amnion 
is  not  clearly  seen,  but  its  extreme  tip  is  indicated  by  the  leader,  p. am.    X  16. 

31.  A  seven  somite  embryo  (I)  of  this  same  vesicle.    For  a  description  of  this 
embryo  see  the  detailed  drawing  shown  in  fig.  15.    X  16. 

32.  The  dorsal  view  of  the  vesicle  reconstructed  in  detail  in  fig.  14.    The  cervix 
end  is  slightly  torn  and  is  turned  under,  consequently  the  common  amnion  and  its 
canals  are  not  shown  in  the  photograph.    The  turning  under  of  the  torn  piece  also 
makes  the  vesicle  appear  shorter  than  it  really  is.    At  o.m.  may  be  seen  the  scale- 
like  villi  beginning  to  overgrow  the  lower  portion  of  the  yolk-sac.    X  2.15. 

33.  A  vesicle  cut  open  along  the  mid-ventral  line  and  spread  apart  to  show  the 
pairing  of  the  embryos.    It  will  be  noted  that  the  embryos  are  arranged  so  that  the 
right-hand  pair  (III  and  IV)  is  the  mirrored  image  of  the  left-hand  pair  (I  and  II). 
At  this  stage  the  amnia  are  still  distinct,  and  in  shape  are  oval  with  the  broad  end 
directed  toward  the  fundus.     X  | 


DEVELOPMENT    OF   THE    NINE-BANDED    ARMADILLO. 
H.  H.  NEWMAN  AND  J.  T.  PATTERSON. 


PLATE  II. 


30 


31 


33 


JOURNAL   OF   MORPHOLOGY,   VOL.   21,    NO. 


PLATE  III 

. 

EXPLANATION    OF   FIGURES 

34.  A  view  of  the  fundus  end  of  a  vesicle  which  contained  embryos  measuring 
31  mm.  head  rump  length.4     In  the  portion  of  the  vesicle  lying  within  the  margin 
of  the  placenta  are  seen  four  window-like  spots.    These  are  the  areas  where  the  am- 
nia  come  in  contact  with  the  wall  of  the  vesicle.    The  fundus  end  is  now  practically 
free  of  villi.    X  \ 

35.  A  view  of  the  cervix  end  of  a  vesicle  in  which  the  embryos  measured  31 
mm.    The  clear  yolk-sac  is  seen  through  the  opening  in  the  rather  thick  placental 
overgrowth.    The  margin  of  this  opening  represents  the  place  where  the  placenta 
is  attached  to  the  uterine  mucosa  at  the  cervix  end  of  the  uterus.    X  f 

36.  The  dorsal  view  of  a  vesicle  which  is  still  attached  to  the  cervix  of  the  con- 
tracted uterus.    This  vesicle  shows  a  distinct  placental  bridge  (p.6.)  connecting 
the  lateral  placentae,  and  also  a  number  of  blood  vessels  at  the  fundus  end.    Em- 
bryos 32  mm.  in  length.     X  f 

37.  A  view  of  the  fundus  end  of  a  vesicle  which  contained  embryos  measuring 
33  mm.    This  view  shows  two  points  worthy  of  especial  note:    (1)  the  four-lobed 
appearance  of  the  fundus  membrane,  due  to  constrictions  occurring  between  the 
fundus  areas  of  the  individual  embryos  (seen  more  clearly  before  fixation) ;  (2) 
the  persistence  of  a  few  villi,  which  in  the  photograph  appear  as  scattering  black 
specks.     X  f 

38.  A  view  of  the  ventral  side  of  vesicle,  with  embryos  measuring  36  mm.    The 
cervix  end  of  the  yolk-sac  is  clearly  visible,  and  blood  vessels  are  seen  at  the  fundus 
end.     The  placental  bridge  although  present   is  not  clearly  brought  out  in  the 
photograph.    X  I 

39.  A  view  of  the  ventral  side  of  a  vesicle  which  contains  embryos  measuring 
53  mm.     The  division  of  the  zone-like  placenta  into  right  and  left  halves  is  clearly 
brought  out.     The  fundus  end  of  the  vesicle  is  now  practically  free  of  both  villi 
and  blood  vessels,  and  the  membranous  area  at  the  cervix  is  much  larger  than  in 
the  preceding  figure.     X  § 


4Unless  otherwise  stated,  the  length  of  the  embryo  will  mean  the  head-rump 
measurement. 


DEVELOPMENT    OF    THE    NINE-BANDED    ARMADILLO. 
H.  H.  NEWMAN  AND  J.  T.  PATTERSON. 


PLATE    III. 


34 


35 


37 


JOITRNAL    OF   MORPHOLOGY,   VOL.  21,    NO.  3. 


PLATE  IV 

EXPLANATION   OF   FIGURES 

40.  The  dorsal  view  of  a  vesicle  in  a  rather  advanced  stage  of  development. 
The  embryos  measure  155  mm.  from  tip  to  tip.    The  dorsal  notch,  d.n.,  although 
extending  down  to  near  the  meddle  of  the  vesicle,  does  not  completely  separate 
the  lateral  placental  discs.    X  f 

41.  Dorsal  view  of  a  vesicle  showing  the  difinitive  condition  of  the  placenta. 
The  placenta  is  divided  into  two  lateral  discs,  each  of  which  is  distinctly  bilobed. 
The  notch  between  the  two  lobes  of  the  left  lateral  (on  right)  disc  is  clearly  shown 
in  the  photograph  (n.l.l.).    The  discs  are  united  to  each  other  both  on  the  dorsal 
and  ventral  side  by  placental  bridges,  the  one  on  the  dorsal  side  (d.b.)  being  the 
narrower.    The  original  arborescent  villi  at  the  cervix  end  have  greatly  degen- 
erated, and  have  become  reduced  to  flat,  blunt  knobs.    The  embryos  in  this  vesicle 
are  about  210  mm.  from  tip  to  tip.     X  \. 

42.  Right  lateral  view  of  a  uterus  showing  a  dorso-ventral  bilobing.    Embryos 
are  48  mm.  long.    X  |r. 

43.  Ventral  view  of  a  pear-shaped  uterus,  which  contained  embryos  measuring 
52  mm.    This  and  the  preceding  uterus  show  two  of  the  several  forms  that  have 
been  observed.  X  \ 


DEVELOPMENT    OF   THE    NINE-BANDED    ARMADILLO. 
H.   H.  NEWMAN  AND  J.  T.  PATTERSON. 


PLATE  IV. 


n.l.L 


42 


43 


JOURNAL   OF   MORPHOLOGY,   VOL.  21,    NO.   3. 


PLATE  V 

EXPLANATION   OF   FIGURES 

44.  A  vesicle  split  open  to  show  the  internal  relationships  of  the  different  parts. 
The  amniotic  connecting  canals  are  seen  to  pass  from  the  anterior  ends  of  the  amnia 
to  the  spot  occupied  by  the  common  amnion.    This  vesicle  also  shows  a  supernu- 
merary canal  (s.aw.c.c.)  extending  from  a  small  vesicle  in  the  Trager  wall  to  the 
canal  belonging  to  the  lower,  right-hand  embryo.    In  the  entire  condition  the  vesi- 
cle measured  24  mm.  wide  by  29  mm.  long,    (see  fig.  3  for  a  diagram  of  the  placenta.) 
Very  slightly  enlarged. 

45.  A  vesicle  laid  open  in  a  manner  similar  to  the  preceding.    At  the  distal  end 
of  each  canal  is  shown  a  series  of  bead-like  enlargements  (c.e.).    The  origin  of  the 
canal  from  the  anterior  tip  of  the  amnion  is  shown  with  especial  clearness  in  the 
embryo  lying  nearest  the  foot  of  the  plate.    In  the  entire  condition  the  vesicle 
measured  24  mm.  wide  and  30  mm.  long.    Very  slightly  enlarged. 


DEVELOPMENT   OF  THE   NINE-BANDED   ARMADILLO. 
H.  H.  NEWMAN  AND  J.  T.  PATTERSON. 


PLATE   V. 


44 


JOURNAL     OF   MORPHOLOGY,   VOL.   21,    NO.   3. 


PLATE  VI 

EXPLANATION   OF  FIGURES 

46.  A  vesicle  cut  open  along  the  mid-ventral  line  to  show  the  relationship  of 
the  embryos  to  each  other  and  to  the  wall  of  the  vesicle.    Each  of  the  four  amniotic 
partitions  (a),  which  have  been  cut  off  close  to  the  chorionic  wall,  lies  just  to  the 
left  of  the  umbilical  cord.    These  are  attached  to  the  wall  near  the  tips  of  the 
placental  lobes  at  the  f undus  end.    The  left  lateral  placental  disc  is  indistinctly 
seen  thiough  the  chorionic  wall,  and  the  notch  separating   it   from  the  right 
lateral  disc  is  marked  with  the  larger  "n",  while  that  indicating  its  division  into 
the  two  lobes  is  designated  by  the  smaller  "n,"  X  |. 

47.  A  photograph  of*  vesicle  no.    108,  which  contained  five  embryos.     This 
vesicle  was  cut  open  along  the  mid-ventral  line.    Embryos  nos.  I,  II,  and  II,  are 
attached  to  the  large,  right  lateral  placental  disc,  and  embryos  III  and  IV  to  the 
smaller,  left  lateral.    (See  text  for  a  fuller  description  and  significance.)    X  £. 


DEVELOPMENT    OF   THE    NINE-BANDED    ARMADILLO. 
H.  H.  NEWMAN  AND  J.  T.   PATTERSON. 


PLATE  VI. 


ill 


IV 


JOURNAL   OF   MORPHOLOGY,   VOL.  21,    NO.  3. 


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